[receiver/prometheus] feat: add Prometheus API server

[gracewehner]

Description:

This is a new PR instead of this one: #32646 which has more relevant discussion.
This PR adds the Prometheus API server as part of the Prometheus receiver if enabled through the receiver config.
It supports calling the /config, /targets, /targets/metadata, /scrape_pools, and /metrics paths for more debugging information about the underlying Prometheus scrape manager and discovery manager.

Link to tracking Issue:
open-telemetry/prometheus-interoperability-spec#63

Testing:
Added tests for the prometheus receiver configuration, for each path that the API supports, and for the server shutting down correctly. Also tested out with running the opentelemetry-collector agent with the prometheus receiver.

Documentation:
Added to the prometheus receiver README about how to configure the setting.

[dashpole]

lgtm otherwise

[dashpole]

Sorry for the slow review. Getting back from vacation

[dashpole]

FYI @jesusvazquez

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.

[gracewehner]

Thanks @dashpole I have taken the latest and things look good with the changes. For all the tests to pass, running make gotidy updated other files, but I can revert those and just have the prometheusreceiver changes if that's better

[atoulme]

Please resolve conflicts?

[atoulme]

Please resolve conflicts. All go.mod files of other components should not be touched, afaict.

[gracewehner]

Resolved the conflicts, but the other go.mod files seem to be due to those also depending on the prometheusreceiver in the go.mod, so it's adding indirect dependencies to those files and the go.sum files

[gracewehner]

Thanks @atoulme all tests are passing and there aren't any merge conflicts right now