[Spike] MultiLoggerProvider

[pellared]

Sharing an idea how users can setup multiple log processing pipelines.

MultiLoggerProvider is a composite (fan-out) provider that duplicates its calls to all the passed providers.
It can be used to set up multiple processing pipelines.
For instance, you can use it create separate providers (pipelines) for OTel events and application logs.

This pattern could be used also for Tracing and Metrics.

MultiLoggerProvider depends only on the API so it would be better moved to Contrib to a separate module called e.g. otelmulti. It is more like a convivence helper for the API package. I was thinking if this idea defined in the specification, but I am unsure if there is a good place for it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.4%. Comparing base (7bd1c85) to head (0ebc71f).
Report is 303 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5830     +/-   ##
=======================================
- Coverage   84.5%   84.4%   -0.1%     
=======================================
  Files        272     273      +1     
  Lines      22734   22754     +20     
=======================================
  Hits       19226   19226             
- Misses      3165    3185     +20     
  Partials     343     343             

see 1 file with indirect coverage changes

[pellared]

@open-telemetry/go-approvers, sharing an idea that I come up with when working on #5825.

[pellared]

CC @MSNev