Missing documentation for queues "/metrics" REST API

[This page here](https://buildkite.com/docs/pipelines/best-practices/monitoring-and-observability?utm_source=openai#getting-metrics-out-of-buildkite-pipelines-decision-matrix) says:

> The GraphQL ClusterQueue node exposes a metrics field with connectedAgentsCount, runningJobsCount, waitingJobsCount, and waitTimeSec (min/p50/p95/max). The same data is available through REST API at `/v2/organizations/{org}/clusters/{cluster_uuid}/queues/{queue_uuid}/metrics.`

But the documentation page for [REST API on queues](https://buildkite.com/docs/apis/rest-api/clusters/queues) does not actually list or describe the `/metrics` end point.

We are working on better metrics for queue health and this data would be helpful to have documented.

Start with the REST API on queues page and compare it with the linked monitoring and observability page. Document the /v2/organizations/{org}/clusters/{cluster_uuid}/queues/{queue_uuid}/metrics endpoint and its queue metrics fields; it is done when the REST page describes the endpoint and returned data.

Written by the indexing model from the issue text.