Document new core Prometheus Exporter about documentation

[danotorrey]

@dulanism Sounds good!

[danotorrey]

FYI @bernd. Placeholder for core Prometheus exports docs.

[danotorrey]

@bernd I've added some details on how exporting works to the issue description.

@dulanism Recently, we decided to implement this new core Prometheus Exporting feature for Graylog 4.1 for a customer request. I know that you already have a lot of docs work on your plate for 4.1. Do you have any time to write documentation for this feature too? Please do not hesitate to say no if your list is full. Since I know the functionality well, I can also write some minimal documentation for it too, and request your review. Please let me know what works best for you.

[dulanism]

Hi @danotorrey. Yeah, could you write up something minimal? I added a note in a gdoc to traverse what you write into the draft

[danotorrey]

@dulanism Sounds good. Will do. How should I write up the first draft? Should I add that as a gdoc with screenshots, links etc., and let you add that the docs repo? Happy to add to the docs repo directly also. Let me know what works best for you.

[dulanism]

@danotorrey I can add it to the repos. Send what you have in a Google doc when you're ready. it might be worth our while to have a 15 minute convo too. Thanks!

[danotorrey]

From discussing with @dulanism I will file an initial PR for this directly in the documentation repo.

[danotorrey]

I have started the documentation, and will file a PR shortly.

[danotorrey]

Closed VIA #1166