fix(exporter-metrics-otlp-http): browser OTLPMetricExporter was not passing config to OTLPMetricExporterBase super class

[trentm]

Refs: #5031

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This was pointed out in Slack here: https://cloud-native.slack.com/archives/C01NL1GRPQR/p1736535825217819
My PR copies some of the test blocks from "test/node/OTLPMetricExporter.test.ts" (those that were passing
config to OTLPMetricExporter) over to the platform test file.

/cc @pichlermarc

• I believe we'll want to backport this to the 1.x branch as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.56%. Comparing base (6864c2f) to head (f890b80).

Additional details and impacted files

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##             main    #5331   +/-   ##
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  Coverage   94.56%   94.56%           
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  Files         322      322           
  Lines        8132     8132           
  Branches     1715     1715           
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  Hits         7690     7690           
  Misses        442      442