Creating point-count metric when using otlp exporter

[rafaelwestphal]

Description

This PR creates the point_counter metric when the otlp exporter is used. The underlying metric used by the GCM exporter is not available, so we use the corresponding otel self-metric to calculate it.

Related issue

b/468059325

How has this been tested?

Checklist:

• Unit tests
  • Unit tests do not apply.
  • Unit tests have been added/modified and passed for this PR.
• Integration tests
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  • Integration tests have been added/modified and passed for this PR.
• Documentation
  • This PR introduces no user visible changes.
  • This PR introduces user visible changes and the corresponding documentation change has been made.
• Minor version bump
  • This PR introduces no new features.
  • This PR introduces new features, and there is a separate PR to bump the minor version since the last release already.
  • This PR bumps the version.