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/integration/client.go

@@ -47,6 +47,7 @@ import (
 	user_pb "github.com/zitadel/zitadel/pkg/grpc/user"
 	user_v2 "github.com/zitadel/zitadel/pkg/grpc/user/v2"
 	user_v2beta "github.com/zitadel/zitadel/pkg/grpc/user/v2beta"
+	webkey_v2 "github.com/zitadel/zitadel/pkg/grpc/webkey/v2"
 	webkey_v2beta "github.com/zitadel/zitadel/pkg/grpc/webkey/v2beta"
 )
 
@@ -70,6 +71,7 @@ type Client struct {
 	FeatureV2      feature.FeatureServiceClient
 	UserSchemaV3   userschema_v3alpha.ZITADELUserSchemasClient
 	WebKeyV2Beta   webkey_v2beta.WebKeyServiceClient
+	WebKeyV2       webkey_v2.WebKeyServiceClient
 	IDPv2          idp_pb.IdentityProviderServiceClient
 	UserV3Alpha    user_v3alpha.ZITADELUsersClient
 	SAMLv2         saml_pb.SAMLServiceClient
@@ -110,6 +112,7 @@ func newClient(ctx context.Context, target string) (*Client, error) {
 		FeatureV2:      feature.NewFeatureServiceClient(cc),
 		UserSchemaV3:   userschema_v3alpha.NewZITADELUserSchemasClient(cc),
 		WebKeyV2Beta:   webkey_v2beta.NewWebKeyServiceClient(cc),
+		WebKeyV2:       webkey_v2.NewWebKeyServiceClient(cc),
 		IDPv2:          idp_pb.NewIdentityProviderServiceClient(cc),
 		UserV3Alpha:    user_v3alpha.NewZITADELUsersClient(cc),
 		SAMLv2:         saml_pb.NewSAMLServiceClient(cc),