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/plugin-download.sh

@@ -0,0 +1,21 @@
+echo $(uname -m)
+
+if [ "$(uname)" = "Darwin" ]; then
+  curl -L -o protoc-gen-connect-openapi.tar.gz https://github.com/sudorandom/protoc-gen-connect-openapi/releases/download/v0.18.0/protoc-gen-connect-openapi_0.18.0_darwin_all.tar.gz
+else
+  ARCH=$(uname -m)
+  case $ARCH in
+    x86_64)
+      ARCH="amd64"
+      ;;
+    aarch64|arm64)
+      ARCH="arm64"
+      ;;
+    *)
+      echo "Unsupported architecture: $ARCH"
+      exit 1
+      ;;
+  esac
+  curl -L -o protoc-gen-connect-openapi.tar.gz https://github.com/sudorandom/protoc-gen-connect-openapi/releases/download/v0.18.0/protoc-gen-connect-openapi_0.18.0_linux_${ARCH}.tar.gz
+fi
+tar -xvf protoc-gen-connect-openapi.tar.gz