Document new version of Health Check extension

[tiffany76]

Desired feature or idea: The Health Check extension is currently under redevelopment. Once the new extension is released, we should document it on the Troubleshooting page of the website.

Collector-Contrib issues and PR to track progress of redevelopment:

• https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/26661
• https://github.com/open-telemetry/opentelemetry-collector-contrib/pull/30673

Additional context: See this comment for related discussion.

The following documentation refers to the old Health Check extension and is pasted here for reference. It is not included on the website.

Health Check

The Health Check extension, which by default is available on all interfaces on port 13133, can be used to ensure the Collector is functioning properly. For example:

extensions:
  health_check:
service:
  extensions: [health_check]

It returns a response like the following:

{
  "status": "Server available",
  "upSince": "2020-11-11T04:12:31.6847174Z",
  "uptime": "49.0132518s"
}

cc: @mwear (just FYI)