feat(domain): Instance APIs with relational tables (#10953)

# Which Problems Are Solved

This PR implements the endpoints listed in
https://github.com/zitadel/zitadel/issues/10443 .

# How the Problems Are Solved

The implementation follows the same pattern as the Organization one.
There are no peculiarities to this PR. The `Update`, `Delete` are
implementing the `Commander` interface, while `Get` and `List`
instance(s) endpoints are implementing the `Querier` interace.

# Additional Context

- Closes #10443
- Depends on #10445

backend/v3/api/instance/v2/convert/instance.go

@@ -0,0 +1,52 @@
+package convert
+
+import (
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	"github.com/zitadel/zitadel/backend/v3/domain"
+	"github.com/zitadel/zitadel/cmd/build"
+	instance "github.com/zitadel/zitadel/pkg/grpc/instance/v2beta"
+)
+
+/*
+ * Domain Model to GRPC v2
+ */
+
+func DomainInstanceListModelToGRPCResponse(instances []*domain.Instance) []*instance.Instance {
+	toReturn := make([]*instance.Instance, len(instances))
+
+	for i, inst := range instances {
+		toReturn[i] = DomainInstanceModelToGRPCResponse(inst)
+	}
+
+	return toReturn
+}
+
+func DomainInstanceModelToGRPCResponse(inst *domain.Instance) *instance.Instance {
+	return &instance.Instance{
+		Id:           inst.ID,
+		ChangeDate:   timestamppb.New(inst.UpdatedAt),
+		CreationDate: timestamppb.New(inst.CreatedAt),
+		State:        instance.State_STATE_RUNNING, // TODO(IAM-Marco): Not sure what to put here
+		Name:         inst.Name,
+		Version:      build.Version(),
+		Domains:      domainInstanceDomainListModelToGRPCResponse(inst.Domains),
+	}
+}
+
+func domainInstanceDomainListModelToGRPCResponse(dms []*domain.InstanceDomain) []*instance.Domain {
+	toReturn := make([]*instance.Domain, len(dms))
+	for i, domain := range dms {
+		isGenerated := domain.IsGenerated != nil && *domain.IsGenerated
+		isPrimary := domain.IsPrimary != nil && *domain.IsPrimary
+		toReturn[i] = &instance.Domain{
+			InstanceId:   domain.InstanceID,
+			CreationDate: timestamppb.New(domain.CreatedAt),
+			Domain:       domain.Domain,
+			Primary:      isPrimary,
+			Generated:    isGenerated,
+		}
+	}
+
+	return toReturn
+}

backend/v3/api/instance/v2/convert/instance_test.go

@@ -0,0 +1,204 @@
+package convert
+
+import (
+	"testing"
+	"time"
+
+	"github.com/muhlemmer/gu"
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	"github.com/zitadel/zitadel/backend/v3/domain"
+	instance "github.com/zitadel/zitadel/pkg/grpc/instance/v2beta"
+)
+
+func TestDomainInstanceModelToGRPCResponse(t *testing.T) {
+	// Given
+	t.Parallel()
+
+	now := time.Now().UTC()
+	yesterday := now.AddDate(0, 0, -1)
+
+	inputInstance := &domain.Instance{
+		ID:        "instance-1",
+		Name:      "Instance One",
+		CreatedAt: yesterday,
+		UpdatedAt: now,
+		Domains: []*domain.InstanceDomain{
+			{
+				InstanceID: "instance-1",
+				Domain:     "d1.example.com",
+				IsPrimary:  gu.Ptr(true),
+				CreatedAt:  yesterday,
+			},
+			{
+				InstanceID:  "instance-1",
+				Domain:      "d2.example.com",
+				IsGenerated: gu.Ptr(true),
+				CreatedAt:   yesterday,
+			},
+			{
+				InstanceID:  "instance-1",
+				Domain:      "d3.example.com",
+				IsPrimary:   gu.Ptr(true),
+				IsGenerated: gu.Ptr(false),
+				CreatedAt:   yesterday,
+			},
+			{
+				InstanceID:  "instance-1",
+				Domain:      "d4.example.com",
+				IsPrimary:   gu.Ptr(false),
+				IsGenerated: gu.Ptr(true),
+				CreatedAt:   yesterday,
+			},
+		},
+	}
+
+	expectedInstance := &instance.Instance{
+		Id:           "instance-1",
+		ChangeDate:   timestamppb.New(now),
+		CreationDate: timestamppb.New(yesterday),
+		State:        instance.State_STATE_RUNNING,
+		Name:         "Instance One",
+		Version:      "",
+		Domains: []*instance.Domain{
+			{
+				InstanceId:   "instance-1",
+				CreationDate: timestamppb.New(yesterday),
+				Domain:       "d1.example.com",
+				Primary:      true,
+				Generated:    false,
+			},
+			{
+				InstanceId:   "instance-1",
+				CreationDate: timestamppb.New(yesterday),
+				Domain:       "d2.example.com",
+				Primary:      false,
+				Generated:    true,
+			},
+			{
+				InstanceId:   "instance-1",
+				CreationDate: timestamppb.New(yesterday),
+				Domain:       "d3.example.com",
+				Primary:      true,
+				Generated:    false,
+			},
+			{
+				InstanceId:   "instance-1",
+				CreationDate: timestamppb.New(yesterday),
+				Domain:       "d4.example.com",
+				Primary:      false,
+				Generated:    true,
+			},
+		},
+	}
+
+	// Test
+	res := DomainInstanceModelToGRPCResponse(inputInstance)
+
+	// Verify
+	assert.Equal(t, expectedInstance, res)
+}
+
+func TestDomainInstanceListModelToGRPCResponse(t *testing.T) {
+	t.Parallel()
+	now := time.Now()
+
+	tt := []struct {
+		testName       string
+		inputResult    []*domain.Instance
+		expectedResult []*instance.Instance
+	}{
+		{
+			testName:       "empty result",
+			inputResult:    []*domain.Instance{},
+			expectedResult: []*instance.Instance{},
+		},
+		{
+			testName: "single instance without domains",
+			inputResult: []*domain.Instance{
+				{
+					ID:        "instance1",
+					Name:      "test-instance",
+					CreatedAt: now,
+					UpdatedAt: now,
+					Domains:   nil,
+				},
+			},
+			expectedResult: []*instance.Instance{
+				{
+					Id:           "instance1",
+					Name:         "test-instance",
+					CreationDate: timestamppb.New(now),
+					ChangeDate:   timestamppb.New(now),
+					State:        instance.State_STATE_RUNNING,
+					Domains:      []*instance.Domain{},
+				},
+			},
+		},
+		{
+			testName: "multiple instances with domains",
+			inputResult: []*domain.Instance{
+				{
+					ID:        "instance1",
+					Name:      "test-instance-1",
+					CreatedAt: now,
+					UpdatedAt: now,
+					Domains: []*domain.InstanceDomain{
+						{
+							InstanceID:  "instance1",
+							Domain:      "domain1.com",
+							CreatedAt:   now,
+							IsPrimary:   gu.Ptr(true),
+							IsGenerated: gu.Ptr(false),
+						},
+					},
+				},
+				{
+					ID:        "instance2",
+					Name:      "test-instance-2",
+					CreatedAt: now,
+					UpdatedAt: now,
+					Domains:   nil,
+				},
+			},
+			expectedResult: []*instance.Instance{
+				{
+					Id:           "instance1",
+					Name:         "test-instance-1",
+					CreationDate: timestamppb.New(now),
+					ChangeDate:   timestamppb.New(now),
+					State:        instance.State_STATE_RUNNING,
+					Domains: []*instance.Domain{
+						{
+							InstanceId:   "instance1",
+							Domain:       "domain1.com",
+							CreationDate: timestamppb.New(now),
+							Primary:      true,
+							Generated:    false,
+						},
+					},
+				},
+				{
+					Id:           "instance2",
+					Name:         "test-instance-2",
+					CreationDate: timestamppb.New(now),
+					ChangeDate:   timestamppb.New(now),
+					State:        instance.State_STATE_RUNNING,
+					Domains:      []*instance.Domain{},
+				},
+			},
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.testName, func(t *testing.T) {
+			t.Parallel()
+			// Test
+			result := DomainInstanceListModelToGRPCResponse(tc.inputResult)
+
+			// Verify
+			assert.Equal(t, tc.expectedResult, result)
+		})
+	}
+}