Add prometheus-emitter docs (#11618)
Add prometheus-emitter docs (#11618)

* Add prometheus-emitter docs

* Update docs/development/extensions.md

Co-authored-by: Charles Smith <5dcb72a123ff9c3f93be52b236fab0b598684c28@gmail.com>

Co-authored-by: Charles Smith <5dcb72a123ff9c3f93be52b236fab0b598684c28@gmail.com>
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