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/server/server.go

@@ -2,11 +2,14 @@ package server
 
 import (
 	"crypto/tls"
+	"net/http"
 
+	"connectrpc.com/connect"
 	grpc_middleware "github.com/grpc-ecosystem/go-grpc-middleware"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
 	healthpb "google.golang.org/grpc/health/grpc_health_v1"
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
 
 	"github.com/zitadel/zitadel/internal/api/authz"
 	grpc_api "github.com/zitadel/zitadel/internal/api/grpc"
@@ -19,21 +22,36 @@ import (
 )
 
 type Server interface {
-	RegisterServer(*grpc.Server)
-	RegisterGateway() RegisterGatewayFunc
 	AppName() string
 	MethodPrefix() string
 	AuthMethods() authz.MethodMapping
 }
 
+type GrpcServer interface {
+	Server
+	RegisterServer(*grpc.Server)
+}
+
+type WithGateway interface {
+	Server
+	RegisterGateway() RegisterGatewayFunc
+}
+
 // WithGatewayPrefix extends the server interface with a prefix for the grpc gateway
 //
 // it's used for the System, Admin, Mgmt and Auth API
 type WithGatewayPrefix interface {
-	Server
+	GrpcServer
+	WithGateway
 	GatewayPathPrefix() string
 }
 
+type ConnectServer interface {
+	Server
+	RegisterConnectServer(interceptors ...connect.Interceptor) (string, http.Handler)
+	FileDescriptor() protoreflect.FileDescriptor
+}
+
 func CreateServer(
 	verifier authz.APITokenVerifier,
 	systemAuthz authz.Config,