Add support for the BMS monitored resource to the Prometheus receiver

[ghost]

Description

The PR adds support for the BMS monitored resource to the Prometheus receiver.

Related issue

b/266788401, b/267347168

How has this been tested?

Manually tested on the test BMS machine using the following steps:

1. Ran the json_exporter on the test BMS machine following this guide
2. Compiled the google_cloud_ops_agent_engine binary and placed it into /opt/google-cloud-ops-agent/libexec/google_cloud_ops_agent_engine on the test BMS machine and restarted the agent.
3. Navigated to Pantheon to confirm that the metrics show up in the Metrics Explorer
   

Checklist:

• Unit tests
  • Unit tests do not apply.
  • Unit tests have been added/modified and passed for this PR.
• Integration tests
  • Integration tests do not apply.
  • 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.

[ghost]

@igorpeshansky I apologize but seems like I accidentally synced my fork with upstream using the github UI, which resulted in the inclusion of some changes from the master branch.

[igorpeshansky]

We should be able to merge those changes into the target branch (bms-support) as well. Or you could undo the merge and force-push. Let me know which you prefer.

[ghost]

It's all done. The merge conflict has been resolved. PTAL ?

[igorpeshansky]

LGTM