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/query.go

@@ -5,11 +5,17 @@ import (
 
 	"connectrpc.com/connect"
 
+	instancev2 "github.com/zitadel/zitadel/backend/v3/api/instance/v2"
+	"github.com/zitadel/zitadel/internal/api/authz"
 	filter "github.com/zitadel/zitadel/internal/api/grpc/filter/v2beta"
 	instance "github.com/zitadel/zitadel/pkg/grpc/instance/v2beta"
 )
 
-func (s *Server) GetInstance(ctx context.Context, _ *connect.Request[instance.GetInstanceRequest]) (*connect.Response[instance.GetInstanceResponse], error) {
+func (s *Server) GetInstance(ctx context.Context, request *connect.Request[instance.GetInstanceRequest]) (*connect.Response[instance.GetInstanceResponse], error) {
+	if authz.GetFeatures(ctx).EnableRelationalTables {
+		return instancev2.GetInstance(ctx, request)
+	}
+
 	inst, err := s.query.Instance(ctx, true)
 	if err != nil {
 		return nil, err
@@ -21,6 +27,10 @@ func (s *Server) GetInstance(ctx context.Context, _ *connect.Request[instance.Ge
 }
 
 func (s *Server) ListInstances(ctx context.Context, req *connect.Request[instance.ListInstancesRequest]) (*connect.Response[instance.ListInstancesResponse], error) {
+	if authz.GetFeatures(ctx).EnableRelationalTables {
+		return instancev2.ListInstances(ctx, req)
+	}
+
 	queries, err := ListInstancesRequestToModel(req.Msg, s.systemDefaults)
 	if err != nil {
 		return nil, err