feat: implement user schema management (#7416)

This PR adds the functionality to manage user schemas through the new user schema service.
It includes the possibility to create a basic JSON schema and also provides a way on defining permissions (read, write) for owner and self context with an annotation.

Further annotations for OIDC claims and SAML attribute mappings will follow.

A guide on how to create a schema and assign permissions has been started. It will be extended though out the process of implementing the schema and users based on those.

Note:
This feature is in an early stage and therefore not enabled by default. To test it out, please enable the UserSchema feature flag on your instance / system though the feature service.

internal/api/grpc/user/schema/v3alpha/server.go

@@ -0,0 +1,51 @@
+package schema
+
+import (
+	"google.golang.org/grpc"
+
+	"github.com/zitadel/zitadel/internal/api/authz"
+	"github.com/zitadel/zitadel/internal/api/grpc/server"
+	"github.com/zitadel/zitadel/internal/command"
+	"github.com/zitadel/zitadel/internal/query"
+	schema "github.com/zitadel/zitadel/pkg/grpc/user/schema/v3alpha"
+)
+
+var _ schema.UserSchemaServiceServer = (*Server)(nil)
+
+type Server struct {
+	schema.UnimplementedUserSchemaServiceServer
+	command *command.Commands
+	query   *query.Queries
+}
+
+type Config struct{}
+
+func CreateServer(
+	command *command.Commands,
+	query *query.Queries,
+) *Server {
+	return &Server{
+		command: command,
+		query:   query,
+	}
+}
+
+func (s *Server) RegisterServer(grpcServer *grpc.Server) {
+	schema.RegisterUserSchemaServiceServer(grpcServer, s)
+}
+
+func (s *Server) AppName() string {
+	return schema.UserSchemaService_ServiceDesc.ServiceName
+}
+
+func (s *Server) MethodPrefix() string {
+	return schema.UserSchemaService_ServiceDesc.ServiceName
+}
+
+func (s *Server) AuthMethods() authz.MethodMapping {
+	return schema.UserSchemaService_AuthMethods
+}
+
+func (s *Server) RegisterGateway() server.RegisterGatewayFunc {
+	return schema.RegisterUserSchemaServiceHandler
+}