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

internal/api/grpc/instance/v2beta/instance.go

@@ -6,10 +6,16 @@ import (
 	"connectrpc.com/connect"
 	"google.golang.org/protobuf/types/known/timestamppb"
 
+	instancev2 "github.com/zitadel/zitadel/backend/v3/api/instance/v2"
+	"github.com/zitadel/zitadel/internal/api/authz"
 	instance "github.com/zitadel/zitadel/pkg/grpc/instance/v2beta"
 )
 
 func (s *Server) DeleteInstance(ctx context.Context, request *connect.Request[instance.DeleteInstanceRequest]) (*connect.Response[instance.DeleteInstanceResponse], error) {
+	if authz.GetFeatures(ctx).EnableRelationalTables {
+		return instancev2.DeleteInstance(ctx, request)
+	}
+
 	obj, err := s.command.RemoveInstance(ctx, request.Msg.GetInstanceId())
 	if err != nil {
 		return nil, err
@@ -22,6 +28,10 @@ func (s *Server) DeleteInstance(ctx context.Context, request *connect.Request[in
 }
 
 func (s *Server) UpdateInstance(ctx context.Context, request *connect.Request[instance.UpdateInstanceRequest]) (*connect.Response[instance.UpdateInstanceResponse], error) {
+	if authz.GetFeatures(ctx).EnableRelationalTables {
+		return instancev2.UpdateInstance(ctx, request)
+	}
+
 	obj, err := s.command.UpdateInstance(ctx, request.Msg.GetInstanceName())
 	if err != nil {
 		return nil, err