[chore] Remove telemetry.useOtelForInternalMetrics stable feature gate

[atoulme]

Description:
Remove the stable feature gate telemetry.useOtelForInternalMetrics. It was declared stable in 0.95.0.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.97%. Comparing base (7198451) to head (07cc29e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9752      +/-   ##
==========================================
- Coverage   90.99%   90.97%   -0.02%     
==========================================
  Files         353      353              
  Lines       18614    18614              
==========================================
- Hits        16937    16934       -3     
- Misses       1352     1354       +2     
- Partials      325      326       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mx-psi]

cc @codeboten

[mx-psi]

cc @codeboten

[mx-psi]

Not sure how I approved twice, lol

[codeboten]

This should have a changelog with breaking change right? as users will no longer be able to specify the feature gate

[atoulme]

I wasn't sure. I looked at previous removal of stable feature gate and it had no changelog entry.

[codeboten]

Right, i think it should always be in the changelog, otherwise the collector won't start with:

Error: invalid argument

[TylerHelmuth]

Since the gate is already stable removing it is a non-breaking change. Since it is stable already, the collector will error on startup if any user attempts to set the gate to any value, so at this point all users should have removed the gate from their startup flags or the collector wont start.

[TylerHelmuth]

Example: open-telemetry/opentelemetry-collector-contrib#28659

[codeboten]

@TylerHelmuth right, but the collector would continue to start until this change goes out no? isn't that what makes it a breaking change?

[TylerHelmuth]

but the collector would continue to start until this change goes out

Well I didnt think it did but I was wrong. So ya, we need a changelog.

[atoulme]

I'll add a changelog, one moment.