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>

docs/package.json

@@ -18,7 +18,8 @@
     "generate:apidocs": "docusaurus gen-api-docs all",
     "generate:configdocs": "cp -r ../cmd/defaults.yaml ./docs/self-hosting/manage/configure/ && cp -r ../cmd/setup/steps.yaml ./docs/self-hosting/manage/configure/",
     "generate:re-gen": "yarn generate:clean-all && yarn generate",
-    "generate:clean-all": "docusaurus clean-api-docs all"
+    "generate:clean-all": "docusaurus clean-api-docs all",
+    "postinstall": "sh ./plugin-download.sh"
   },
   "dependencies": {
     "@bufbuild/buf": "^1.14.0",