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/v2beta/user_test.go

@@ -322,7 +322,9 @@ func Test_idpIntentToIDPIntentPb(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			got, err := idpIntentToIDPIntentPb(tt.args.intent, tt.args.alg)
 			require.ErrorIs(t, err, tt.res.err)
-			grpc.AllFieldsEqual(t, tt.res.resp.ProtoReflect(), got.ProtoReflect(), grpc.CustomMappers)
+			if tt.res.resp != nil {
+				grpc.AllFieldsEqual(t, tt.res.resp.ProtoReflect(), got.Msg.ProtoReflect(), grpc.CustomMappers)
+			}
 		})
 	}
 }