API: expose per-container resource usage (memory/CPU), including Docker Compose services

[FaberVi]

Hi! We run several Docker Compose stacks on Coolify and manage them only through the REST API. Today the API doesn't return any resource usage, and for compose services there are no metrics in the UI either.

What we'd like is a read-only endpoint that returns current usage per container on a server, compose services included. For example:

GET /api/v1/servers/{uuid}/containers/metrics

For each container it would return the name, the linked resource (application, database or service and its uuid), CPU %, memory used and limit in bytes, memory used %, and a timestamp. An optional ?container=<name>&minutes=N could return the history, which is useful to see the peak. It would need only the read ability, and the Sentinel token would never leave the server.

It looks like most of the pieces are already there in release/v4.5 (SentinelMetricsClient::containersCurrent()). This would extend #11431 / #11432, which cover server-level metrics only.

Our use case is sizing mem_limit from real usage after a deploy: we raise the limit when usage stays above about 80% and lower it below about 30%. Today we have to read docker stats by hand on the server.

If this direction is welcome, I'm happy to open a PR against release/v4.5 with the endpoint, the OpenAPI docs and tests.