[EXPORTER] fix throw in OtlpGrpcMetricExporter with shared grpc client

[dbarker]

Fixes #3242

OtlpGrpcMetricExporter throws on export when constructed with a shared grpc client.

Changes

• Sets the OtlpGrpcMetricExporter::aggregation_temporality_selector_ in the constructors that accept a shared grpc client
• Adds test cases to cover OtlpGrpcMetricExporter::GetAggregationTemporality

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.16%. Comparing base (57114c5) to head (d321ae1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3243   +/-   ##
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  Coverage   88.16%   88.16%           
=======================================
  Files         198      198           
  Lines        6224     6224           
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  Hits         5487     5487           
  Misses        737      737           

[lalitb]

LGTM. Thanks.

[owent]

LGTM, thanks.

[marcalff]

LGTM, thanks for the fix.