feat(otel): GA for cmake

[dbolduc]

Part of the work for #12726

I think we need to wait until our vcpkg port has been updated before changing that part of the docs:

google-cloud-cpp/google/cloud/opentelemetry/quickstart/README.md

Line 168 in f251ffc

./vcpkg install google-cloud-cpp[core,experimental-opentelemetry,storage]

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This change is 

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (f251ffc) 93.58% compared to head (269a29d) 93.58%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12735   +/-   ##
=======================================
  Coverage   93.58%   93.58%           
=======================================
  Files        2075     2075           
  Lines      183586   183586           
=======================================
+ Hits       171806   171809    +3     
+ Misses      11780    11777    -3     

see 5 files with indirect coverage changes

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[coryan]

Should we include opentelemetry in GOOGLE_CLOUD_CPP_GA_LIBRARIES? I think we should.

[dbolduc]

1. If we were to do this, s/GA/TRANSITION/
2. It would take some modifications. e.g. there is no mocks library

   google-cloud-cpp/BUILD.bazel

   Lines 89 to 98 in f251ffc

   	[cc_library(
   	name = "{library}_mocks".format(library = library),
   	testonly = True,
   	deps = [
   	"//google/cloud/{library_dir}:google_cloud_cpp_{library}_mocks".format(
   	library = library,
   	library_dir = google_cloud_cpp_library_dir_name(library),
   	),
   	],
   	) for library in GA_LIBRARIES + TRANSITION_LIBRARIES]

This may simplify things though. I will experiment.

[coryan]

Feel free to merge as-is while you experiment with a better alternative.