Consistency update for TOCs of manual instrumentation pages

[svrnm]

Another consistency update for the manual instrumentation pages. After this PR gets merged:

• all languages more or less have the same structure:

  Setup
  Traces
  Metrics
  Logs
  ...
  Next Steps
  

• if a signal is not yet stable or documentation is missing, this is called out in place. if the signal is stable, readers are asked to contribute
• Moved the section about OTLP Exporter for erlang to a separate page to follow the structure of other languages
• Some other structural updates to create consistency

[cartermp]

Overall LGTM, just wondering why some files don't have a top-level Setup section? e.g., .NET

[svrnm]

Overall LGTM, just wondering why some files don't have a top-level Setup section? e.g., .NET

That's a task for another update. I added some where possible, but that might need some extra work to create this consistently.

[cartermp]

Sounds good!