Refactor logstash -> monitoring dependency to use plugin contracts instead of HTTP

[joshdover]

In the logstash plugin, there is an integration with Stack Monitoring that currently relies on an internal monitoring HTTP API: #63417 (comment)

After #62908 is completed, this should be refactored so that the monitoring plugin exposes a JavaScript API over this HTTP endpoint that the logstash plugin can call directly via the plugin contract.

[smith]

Not prioritizing this at this time.