feat(domain): introduce error slugs (#12030)

# Which Problems Are Solved

As part of https://github.com/zitadel/zitadel/issues/11917 we want to
introduce error slugs so (API) clients can rely on stable,
machine-readable errors and act accordingly.

# How the Problems Are Solved

- Added a `NewSlug` helper function in the domain package.
- Added `ErrorDetails` to the `ZitadelError`
- Added an `zitadel.error.v2.ErrorDetail` proto message
- Updated the connectRPC error interceptor to map new slug based errors
to the new `ErrorDetail`
- Defined some common slugs and error functions like internal errors
- Defined (session) specific slugs used in the `DeleteSession` and
`CheckUser` functions and replaced old implementations
- Updated integration tests to check specific errors if the relation
database feature is enabled
- Updated doc and guideline to reflect the latest changes and decisions
- Updated DeleteSession endpoint API to list possible slugs

# Additional Changes

None

# Additional Context

- closes #11957

---------

Co-authored-by: Wim Van Laer <[email protected]>

internal/integration/assert.go

@@ -12,6 +12,8 @@ import (
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/timestamppb"
 
+	"github.com/zitadel/zitadel/internal/api/grpc/gerrors"
+	errorpb "github.com/zitadel/zitadel/pkg/grpc/error/v2"
 	metadata "github.com/zitadel/zitadel/pkg/grpc/metadata/v2"
 	resources_object "github.com/zitadel/zitadel/pkg/grpc/resources/object/v3alpha"
 )
@@ -191,3 +193,59 @@ func getMetadataMap(metadataEntries []*metadata.Metadata) map[string][]byte {
 	}
 	return metadataByKey
 }
+
+func RequireStatusError(t *testing.T, err, targetErr error) {
+	t.Helper()
+
+	if AssertStatusError(t, err, targetErr) {
+		return
+	}
+	t.FailNow()
+}
+
+func AssertStatusError(t *testing.T, err, targetErr error) bool {
+	t.Helper()
+
+	cErr, ok := status.FromError(err)
+	if !ok {
+		return assert.Fail(t, "expected status error")
+	}
+
+	tErr, ok := status.FromError(gerrors.ZITADELToGRPCError(t.Context(), targetErr))
+	if !ok {
+		return assert.Fail(t, "expected status error")
+	}
+	if !assert.Equal(t, tErr.Code(), cErr.Code(), "expected different status code") {
+		return false
+	}
+	if len(tErr.Details()) == 1 {
+		if len(cErr.Details()) != 1 {
+			return assert.Fail(t, "missing details")
+		}
+		targetDetails, ok := tErr.Details()[0].(*errorpb.ErrorDetail)
+		if !ok {
+			return assert.Failf(t, "expected error detail in target error", "got %#v", tErr.Details()[0])
+		}
+		details, ok := cErr.Details()[0].(*errorpb.ErrorDetail)
+		if !ok {
+			return assert.Failf(t, "expected error detail in actual error", "got %#v", cErr.Details()[0])
+		}
+		return AssertErrorDetail(t, details, targetDetails)
+	}
+	return true
+}
+
+func AssertErrorDetail(t *testing.T, detail, targetDetail *errorpb.ErrorDetail) bool {
+	t.Helper()
+
+	if !assert.Equal(t, targetDetail.GetSlug(), detail.GetSlug(), "expected different slug") {
+		return false
+	}
+	if targetDetail.GetMessage() != "" && !assert.Equal(t, targetDetail.GetMessage(), detail.GetMessage(), "expected different message") {
+		return false
+	}
+	if targetDetail.GetDetails() != nil && !assert.Equal(t, targetDetail.GetDetails().AsMap(), detail.GetDetails().AsMap(), "expected different details") {
+		return false
+	}
+	return true
+}