Add gRPC examples with OTLP SDK

[damemi]

Uses our basic examples with gRPC application default credential functions to send OTLP

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fda999e) 69.94% compared to head (13f76b5) 70.22%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #800      +/-   ##
==========================================
+ Coverage   69.94%   70.22%   +0.28%     
==========================================
  Files          42       42              
  Lines        4877     4886       +9     
==========================================
+ Hits         3411     3431      +20     
+ Misses       1315     1307       -8     
+ Partials      151      148       -3     

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[dashpole]

any reason why the trace sample is in a client subdirectory, but the metric one isn't?

[damemi]

any reason why the trace sample is in a client subdirectory, but the metric one isn't?

It's not referring to the otlp client, it's 2 directories, client and server just copied from our existing example https://github.com/GoogleCloudPlatform/opentelemetry-operations-go/tree/266b13738059ce0f18feef3e5b7e235c48d0065c/example/trace/http

edit: simplified it down to one file with a time.sleep