Disable OpenTelemetry metrics

[adriansmares]

Summary

References open-telemetry/opentelemetry-go-contrib#5190
References #5692

This PR disables OpenTelemetry metrics (which we don't use), and remove some long standing technical debt.

Changes

• Remove OpenCensus as a dependency.
  • OpenCensus is now defunct, and it is replaced by OpenTelemetry completely.
  • We didn't really use the metrics exposed by OpenCensus, so this is safe to do.
• Skip metric creation in OpenTelemetry integrations.
  • pkg/metrics is Prometheus based and it is currently not exposing these metrics, so we don't need them.
  • At the same time, current metrics are leaky (see the referenced issue), so disabling them is required even.

Testing

Local testing with the /metrics endpoint in order to ensure that I am not accidentally taking out useful metrics.

No manual testing required.

Regressions

The OpenCensus hooks were not really used, and I cannot find any OpenCensus metrics in our Prometheus clusters, so we should not have any specific regressions.

Notes for Reviewers

This will be backported to v3.29.1 for the leak fix.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• The steps/process to test this feature are clearly explained including testing for regressions.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.

[adriansmares]

This has been deployed, and confirmed as working.