docs[open-telemetry]: Add specifications for content negotation and escaping, and docs for translation strategies for Otel metric name translation

[ywwg]

This updates the docs to represent the current state of otel configuration options. It also creates specification files to document scraping content negotiation and escaping schemes.

[ArthurSens]

LGTM

[ArthurSens]

Thank you for the effort writing this :)

I have some suggestions 👇

[ArthurSens]

"the system" refers to Prometheus itself? If yes, could we adjust the wording a bit? I think using "it" is already clearer than the system

[ywwg]

yeah I can tweak that. There are cases where the spec isn't necessarily referencing prometheus, it could be referencing an endpoint like the otel SDK. So there are places where we want to be more generic. But I think this one can be switched over.

[ywwg]

I did some more polishing, would appreciate one final look over

[ArthurSens]

[juliusv]

Hey hey, I just saw this as I was launching the new prometheus.io homepage at the Berlin Prometheus meetup and had to merge it into my PR branch for that. I noticed a few things:

• The sort_rank frontmatter fields need to be adjusted relative to their existing sibling documents in the same folder, I took the liberty to fix those in 60c4d88
• The documents are currently under "Concepts", but that top-level menu point is meant for basic Prometheus concepts that every Prometheus beginner should familiarize themselves with. The new docs are more detailed specifications that only some experts need to know, and not something a new Prometheus user should be confronted with. I talked with @beorn7 about it at the meetup as well - how about moving these to "Instrumenting", since they are both about that, and there are similar docs like that already under there? It almost sounds like the two docs are related to the existing "Exposition Formats" doc under there. I wonder if opening a new subsection under "Instrumenting" for all three would make sense, or otherwise combining them somehow?
• The titles of the documents are quite long - that's fine for the page itself, but nav and prev/next pagination buttons weren't really made with such long titles in mind. You can set an alternate title to be shown in the side nav using the nav_title frontmatter field, which could be shorter.

[juliusv]

I'll make a PR with a beginning of a move to the "Instrumenting" section. It does seem like both new sections should be referenced from (if not merged with) https://prometheus.io/docs/instrumenting/exposition_formats/.

[juliusv]

See: #2657