Support unix socket for OTLP with gRPC export of internal telemetry

[dmathieu]

Description

This allows specifying a unix socket for the internal telemetry OTLP endpoint, when using gRPC.

Link to tracking issue

Fixes #11941

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.67%. Comparing base (0ece678) to head (af878b0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12059   +/-   ##
=======================================
  Coverage   91.67%   91.67%           
=======================================
  Files         455      455           
  Lines       24038    24043    +5     
=======================================
+ Hits        22037    22042    +5     
  Misses       1629     1629           
  Partials      372      372           

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[bogdandrutu]

Thanks for this PR @dmathieu

I will let @codeboten jump onto this since we are planning to delete this otelinit and use the contrib config initialization.

@codeboten feel free to dismiss my change request if you are ok with this, I added here only to ensure you see this.

[codeboten]

Thanks @dmathieu, @bogdandrutu is correct, the code in otelinit will be removed completely in favour of the config package once #11611 lands. It's currently waiting on the next release of otel-go and otel-go-contrib to avoid bumping the minimum go version.

It would be great to add a test to the config package to validate that unix sockets are supported