feat(group): group service to create, update, and delete groups (#10455)

# Which Problems Are Solved

This PR adds API definition and backend implementation for GroupService
to manage user groups.

# How the Problems Are Solved
* API definition to create, update, retrieve, and delete groups is added
* Command-side implementation to create, update, and delete user groups
as part of the GroupV2 API is added

# Additional Changes
N/A

# Additional Context
- Related to #10089, #9702 (parent ticket)
- User contribution: https://github.com/zitadel/zitadel/pull/9428/files
- Additional functionalities to list/search user groups, add
permissions, manage users in groups, group scopes will be added in
subsequent PRs.
- Also needs documentation, which will be added once the entire feature
is available

---------

Co-authored-by: Livio Spring <[email protected]>

internal/api/grpc/group/v2/server.go

@@ -0,0 +1,60 @@
+package group
+
+import (
+	"net/http"
+
+	"connectrpc.com/connect"
+	"google.golang.org/protobuf/reflect/protoreflect"
+
+	"github.com/zitadel/zitadel/internal/api/authz"
+	"github.com/zitadel/zitadel/internal/command"
+	"github.com/zitadel/zitadel/internal/config/systemdefaults"
+	"github.com/zitadel/zitadel/internal/domain"
+	"github.com/zitadel/zitadel/internal/query"
+	group_v2 "github.com/zitadel/zitadel/pkg/grpc/group/v2"
+	"github.com/zitadel/zitadel/pkg/grpc/group/v2/groupconnect"
+)
+
+var _ groupconnect.GroupServiceHandler = (*Server)(nil)
+
+type Server struct {
+	systemDefaults systemdefaults.SystemDefaults
+	command        *command.Commands
+	query          *query.Queries
+
+	checkPermission domain.PermissionCheck
+}
+
+func CreateServer(
+	systemDefaults systemdefaults.SystemDefaults,
+	command *command.Commands,
+	query *query.Queries,
+	checkPermission domain.PermissionCheck,
+) *Server {
+	return &Server{
+		systemDefaults:  systemDefaults,
+		command:         command,
+		query:           query,
+		checkPermission: checkPermission,
+	}
+}
+
+func (s *Server) RegisterConnectServer(interceptors ...connect.Interceptor) (string, http.Handler) {
+	return groupconnect.NewGroupServiceHandler(s, connect.WithInterceptors(interceptors...))
+}
+
+func (s *Server) FileDescriptor() protoreflect.FileDescriptor {
+	return group_v2.File_zitadel_group_v2_group_service_proto
+}
+
+func (s *Server) AppName() string {
+	return group_v2.GroupService_ServiceDesc.ServiceName
+}
+
+func (s *Server) MethodPrefix() string {
+	return group_v2.GroupService_ServiceDesc.ServiceName
+}
+
+func (s *Server) AuthMethods() authz.MethodMapping {
+	return group_v2.GroupService_AuthMethods
+}