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/connect_middleware/cache_interceptor.go

@@ -0,0 +1,31 @@
+package connect_middleware
+
+import (
+	"context"
+	"net/http"
+	"time"
+
+	"connectrpc.com/connect"
+
+	_ "github.com/zitadel/zitadel/internal/statik"
+)
+
+func NoCacheInterceptor() connect.UnaryInterceptorFunc {
+	return func(handler connect.UnaryFunc) connect.UnaryFunc {
+		return func(ctx context.Context, req connect.AnyRequest) (connect.AnyResponse, error) {
+			headers := map[string]string{
+				"cache-control": "no-store",
+				"expires":       time.Now().UTC().Format(http.TimeFormat),
+				"pragma":        "no-cache",
+			}
+			resp, err := handler(ctx, req)
+			if err != nil {
+				return nil, err
+			}
+			for key, value := range headers {
+				resp.Header().Set(key, value)
+			}
+			return resp, err
+		}
+	}
+}