impl(GCS+gRPC): export metrics with desired monitored resource

[coryan]

Fixes #13998

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This change is 

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.59%. Comparing base (ee21b70) to head (d5d80b5). Report is 92 commits behind head on main.

Files with missing lines	Patch %	Lines
.../storage/internal/grpc/metrics_exporter_options.cc	0.00%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14270   +/-   ##
=======================================
  Coverage   93.58%   93.59%           
=======================================
  Files        2318     2318           
  Lines      207177   207163   -14     
=======================================
+ Hits       193886   193893    +7     
+ Misses      13291    13270   -21     

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