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/idp_link.go

@@ -3,6 +3,8 @@ package user
 import (
 	"context"
 
+	"connectrpc.com/connect"
+
 	"github.com/zitadel/zitadel/internal/api/grpc/object/v2"
 	"github.com/zitadel/zitadel/internal/command"
 	"github.com/zitadel/zitadel/internal/domain"
@@ -11,22 +13,22 @@ import (
 	"github.com/zitadel/zitadel/pkg/grpc/user/v2"
 )
 
-func (s *Server) AddIDPLink(ctx context.Context, req *user.AddIDPLinkRequest) (_ *user.AddIDPLinkResponse, err error) {
-	details, err := s.command.AddUserIDPLink(ctx, req.UserId, "", &command.AddLink{
-		IDPID:         req.GetIdpLink().GetIdpId(),
-		DisplayName:   req.GetIdpLink().GetUserName(),
-		IDPExternalID: req.GetIdpLink().GetUserId(),
+func (s *Server) AddIDPLink(ctx context.Context, req *connect.Request[user.AddIDPLinkRequest]) (_ *connect.Response[user.AddIDPLinkResponse], err error) {
+	details, err := s.command.AddUserIDPLink(ctx, req.Msg.GetUserId(), "", &command.AddLink{
+		IDPID:         req.Msg.GetIdpLink().GetIdpId(),
+		DisplayName:   req.Msg.GetIdpLink().GetUserName(),
+		IDPExternalID: req.Msg.GetIdpLink().GetUserId(),
 	})
 	if err != nil {
 		return nil, err
 	}
-	return &user.AddIDPLinkResponse{
+	return connect.NewResponse(&user.AddIDPLinkResponse{
 		Details: object.DomainToDetailsPb(details),
-	}, nil
+	}), nil
 }
 
-func (s *Server) ListIDPLinks(ctx context.Context, req *user.ListIDPLinksRequest) (_ *user.ListIDPLinksResponse, err error) {
-	queries, err := ListLinkedIDPsRequestToQuery(req)
+func (s *Server) ListIDPLinks(ctx context.Context, req *connect.Request[user.ListIDPLinksRequest]) (_ *connect.Response[user.ListIDPLinksResponse], err error) {
+	queries, err := ListLinkedIDPsRequestToQuery(req.Msg)
 	if err != nil {
 		return nil, err
 	}
@@ -34,10 +36,10 @@ func (s *Server) ListIDPLinks(ctx context.Context, req *user.ListIDPLinksRequest
 	if err != nil {
 		return nil, err
 	}
-	return &user.ListIDPLinksResponse{
+	return connect.NewResponse(&user.ListIDPLinksResponse{
 		Result:  IDPLinksToPb(res.Links),
 		Details: object.ToListDetails(res.SearchResponse),
-	}, nil
+	}), nil
 }
 
 func ListLinkedIDPsRequestToQuery(req *user.ListIDPLinksRequest) (*query.IDPUserLinksSearchQuery, error) {
@@ -72,14 +74,14 @@ func IDPLinkToPb(link *query.IDPUserLink) *user.IDPLink {
 	}
 }
 
-func (s *Server) RemoveIDPLink(ctx context.Context, req *user.RemoveIDPLinkRequest) (*user.RemoveIDPLinkResponse, error) {
-	objectDetails, err := s.command.RemoveUserIDPLink(ctx, RemoveIDPLinkRequestToDomain(ctx, req))
+func (s *Server) RemoveIDPLink(ctx context.Context, req *connect.Request[user.RemoveIDPLinkRequest]) (*connect.Response[user.RemoveIDPLinkResponse], error) {
+	objectDetails, err := s.command.RemoveUserIDPLink(ctx, RemoveIDPLinkRequestToDomain(ctx, req.Msg))
 	if err != nil {
 		return nil, err
 	}
-	return &user.RemoveIDPLinkResponse{
+	return connect.NewResponse(&user.RemoveIDPLinkResponse{
 		Details: object.DomainToDetailsPb(objectDetails),
-	}, nil
+	}), nil
 }
 
 func RemoveIDPLinkRequestToDomain(ctx context.Context, req *user.RemoveIDPLinkRequest) *domain.UserIDPLink {