feat: exchange gRPC server implementation to connectRPC (#10145)

# Which Problems Are Solved

The current maintained gRPC server in combination with a REST (grpc)
gateway is getting harder and harder to maintain. Additionally, there
have been and still are issues with supporting / displaying `oneOf`s
correctly.
We therefore decided to exchange the server implementation to
connectRPC, which apart from supporting connect as protocol, also also
"standard" gRCP clients as well as HTTP/1.1 / rest like clients, e.g.
curl directly call the server without any additional gateway.

# How the Problems Are Solved

- All v2 services are moved to connectRPC implementation. (v1 services
are still served as pure grpc servers)
- All gRPC server interceptors were migrated / copied to a corresponding
connectRPC interceptor.
- API.ListGrpcServices and API. ListGrpcMethods were changed to include
the connect services and endpoints.
- gRPC server reflection was changed to a `StaticReflector` using the
`ListGrpcServices` list.
- The `grpc.Server` interfaces was split into different combinations to
be able to handle the different cases (grpc server and prefixed gateway,
connect server with grpc gateway, connect server only, ...)
- Docs of services serving connectRPC only with no additional gateway
(instance, webkey, project, app, org v2 beta) are changed to expose that
- since the plugin is not yet available on buf, we download it using
`postinstall` hook of the docs

# Additional Changes

- WebKey service is added as v2 service (in addition to the current
v2beta)

# Additional Context

closes #9483

---------

Co-authored-by: Elio Bischof <elio@zitadel.com>

internal/api/grpc/user/v2/machine.go

@@ -3,6 +3,7 @@ package user
 import (
 	"context"
 
+	"connectrpc.com/connect"
 	"google.golang.org/protobuf/types/known/timestamppb"
 
 	"github.com/zitadel/zitadel/internal/command"
@@ -11,7 +12,7 @@ import (
 	"github.com/zitadel/zitadel/pkg/grpc/user/v2"
 )
 
-func (s *Server) createUserTypeMachine(ctx context.Context, machinePb *user.CreateUserRequest_Machine, orgId, userName, userId string) (*user.CreateUserResponse, error) {
+func (s *Server) createUserTypeMachine(ctx context.Context, machinePb *user.CreateUserRequest_Machine, orgId, userName, userId string) (*connect.Response[user.CreateUserResponse], error) {
 	cmd := &command.Machine{
 		Username:        userName,
 		Name:            machinePb.Name,
@@ -32,21 +33,21 @@ func (s *Server) createUserTypeMachine(ctx context.Context, machinePb *user.Crea
 	if err != nil {
 		return nil, err
 	}
-	return &user.CreateUserResponse{
+	return connect.NewResponse(&user.CreateUserResponse{
 		Id:           cmd.AggregateID,
 		CreationDate: timestamppb.New(details.EventDate),
-	}, nil
+	}), nil
 }
 
-func (s *Server) updateUserTypeMachine(ctx context.Context, machinePb *user.UpdateUserRequest_Machine, userId string, userName *string) (*user.UpdateUserResponse, error) {
+func (s *Server) updateUserTypeMachine(ctx context.Context, machinePb *user.UpdateUserRequest_Machine, userId string, userName *string) (*connect.Response[user.UpdateUserResponse], error) {
 	cmd := updateMachineUserToCommand(userId, userName, machinePb)
 	err := s.command.ChangeUserMachine(ctx, cmd)
 	if err != nil {
 		return nil, err
 	}
-	return &user.UpdateUserResponse{
+	return connect.NewResponse(&user.UpdateUserResponse{
 		ChangeDate: timestamppb.New(cmd.Details.EventDate),
-	}, nil
+	}), nil
 }
 
 func updateMachineUserToCommand(userId string, userName *string, machine *user.UpdateUserRequest_Machine) *command.ChangeMachine {