Unify internal observability documentation and move it to website

[tiffany76]

Fixes open-telemetry/opentelemetry-collector#8886.

This PR brings together three different documents from the Collector repo: Troubleshooting, OpenTelemetry Collector Observability, and Monitoring.

NOTE: Work on this PR is broken up into three smaller pull requests. See bullet list below for corresponding PRs.

Per @mx-psi, this new document should describe:

• How to enable observability (Unify internal observability documentation - 1 of 3 #4246)
• What is our observability offering and what each metric means (Unify internal observability documentation - 2 of 3 #4322)
• How to effectively use this telemetry to monitor the Collector (Unify internal observability documentation - 3 of 3 #4529)

The merged and reworked file will be located on opentelemetry.io, with its precise location in the nav hierarchy and title to be decided.

cc @codeboten

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Preview: https://deploy-preview-4192--opentelemetry.netlify.app/docs/collector/internal-telemetry/

[tiffany76]

This is still a VERY rough draft and very much a WIP. I've broken up the content into sections but done nothing else. Avert your eyes! :)

[theletterf]

Great initiative, @tiffany76 ! For a better review experience, I think it'd be great if you could split the PR into one for each file / concern.

[tiffany76]

Thanks, @theletterf! I will do that next. Traveling this week so progress may be a little slow.

[svrnm]

Great initiative! As mentioned on the related collector issue I am fine with having a troubleshooting and an observability/internal telemetry page, we can talk about the right name eventually.

[chalin]

Some drive-by comments. More copyedits to come when this is no longer in draft mode.

[tiffany76]

For a better review experience, I think it'd be great if you could split the PR into one for each file / concern.

Hi @theletterf and others, I've thought about how best to break this down and have decided to leave this PR here, in draft, with the full content. I'll create new smaller PRs with each of the three sections. The first PR is up (still in draft): #4246.

Hope that works for you!