docs: New APM configuration section

[bmorelli25]

Summary

This PR is mostly structural. It moves the Configure section up two levels in the navigation. This requires many heading-level changes. I also moved all of the configure documentation to a new subdirectory so it's easier to find and edit.

Separating this into its own PR should make the content changes that are coming easier to review.

[mergify]

This pull request does not have a backport label. Could you fix it @bmorelli25? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.x is the label to automatically backport to the 7.x branch.
• backport-7./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[ghost]

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• Start Time: 2023-05-15T23:12:13.148+0000

• Duration: 1 min 59 sec

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[simitt]

I have several comments for the content, but keep them (mostly) for the dedicated content PR. From the structural changes, this LGTM

[simitt]

note on content: we should add that the URL is purely informational, and has no effect on where the server is reachable. For changing where the server is listening, the Host needs to be configured.

@bmorelli25 totally up to you if you want to add this here or in a follow up PR

[bmorelli25]

As discussed offline with Silvia on 10/05/23, I'll address this and all other feedback in the follow-up PR.

[simitt]

The host and max_header_size are duplicated now (as they are also documented in the general section)

[mergify]

This pull request is now in conflicts. Could you fix it @bmorelli25? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b ft-new-config upstream/ft-new-config
git merge upstream/main
git push upstream ft-new-config