Add a monitor for the OpenMetrics endpoint

[willmostly]

Add a monitor for the OpenMetrics endpoint. This populates the running and queued query metrics for active load balancing, and allows defining health using minimum and maximum values for arbitrary metrics.

Description

Add a monitor for the /metrics endpoint. These metrics are equivalent to those under v1/jmx, however some organizations choose to standardize on OpenMetrics instead.

A custom definition of backend health can be configured through the metricMinimumValues and metricMaximumValues settings in monitorConfiguration. Each of these takes metricName, float pairs. If the returned metric is below the min or greater than the max, the backend is considered unhealthy.

Additional context and related issues

Release notes

( ) This is not user-visible or is docs only, and no release notes are required.
( ) Release notes are required. Please propose a release note for me.
(x ) Release notes are required, with the following suggested text:

* Add OpenMetrics health monitor with customizable health definition

[oneonestar]

Just a quick skim.

[oneonestar]

I think e.toString() is better than e.getMessage() .

[willmostly]

UnexpectedResponseException.toString() does not print the message unfortunately. I'll open a PR in airlift to add it and temporarily log both until it is merged and we upgrade. The message contains details about any issues with missing metrics, which could be a common issue given the long names. The error logged with e.getMessage() will be something like

2025-01-08T18:19:41.384+0000 SEVERE Health check failed with non-retryable response. Request is missing required keys: 
trino_execution_name_QueryManager_RunningQueries
trino_execution_name_QueryManager_QueuedQueries
trino_metadata_name_DiscoveryNodeManager_ActiveNodeCount
in response: 'Basic authentication or X-Trino-Original-User or X-Trino-User must be sent'
UnexpectedResponseException{request=GET http://localhost:32835/metrics?name%5B%5D=trino_execution_name_QueryManager_RunningQueries&name%5B%5D=trino_execution_name_QueryManager_QueuedQueries&name%5B%5D=trino_metadata_name_DiscoveryNodeManager_ActiveNodeCount, statusCode=401, headers={Date=[Wed, 08 Jan 2025 18:19:41 GMT], Vary=[Accept-Encoding], Content-Type=[text/plain;charset=UTF-8], WWW-Authenticate=[Basic realm="Trino"], Content-Length=[74]}}

(I removed the user header to trigger an error).

[willmostly]

airlift/airlift#1352