Switch to opampextension for supervision of elastic-otel-collector

[cmacknz]

• Relates Support Unix domain socket transport for client and server open-telemetry/opamp-go#601
• Relates Use opamp for otel collector monitoring #14025
• Relates Run osquerybeat as a receiver by default and route live query actions to it via the diagnostics extension #15459

Complete the proof of concept in #14025 to switch using stdin to provide configuration and the healthcheck extension to retrieve component status to using the opampextension to:

• Provide collector configuration
• Retrieve collector status
• Transport Fleet actions as custom messages replacing the action routing in the diagnostics extension that was added in Run osquerybeat as a receiver by default and route live query actions to it via the diagnostics extension #15459

We will want the OpAMP websocket to operate on a unix domain socket/named pipe as described in open-telemetry/opamp-go#601.

[infra-vault-gh-plugin-prod]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[cmacknz]

@swiatekm pre-emptively assigning to you since you've been looking at this already