enhancement: support proto resources for grpc-transcode workflows

Summary

Please triage whether the controller should support managing proto resources needed by grpc-transcode workflows.

Current behavior

APISIX itself supports proto resources for grpc-transcode through the Admin API, including proto_id references from route plugin configuration, but the current controller API surface does not provide a resource model for defining and delivering those proto descriptors.

The codebase includes grpc-transcode in the runtime plugin set, but there is no corresponding CRD or Gateway API abstraction for proto resource management.

As a result, a grpc-transcode setup that works in APISIX cannot currently be expressed end-to-end through the controller.

Use cases affected

• configuring grpc-transcode end-to-end through the controller, including both the route/plugin configuration and the proto descriptor it depends on
• managing proto descriptors declaratively alongside routes and upstreams, instead of falling back to a separate manual configuration path

Code context

• api/ currently does not expose a proto resource model for this workflow
• the e2e manifests include grpc-transcode in the runtime plugin set, but not a controller resource for proto definitions