[Draft] Add TestAppHubLogLabels to test AppHub integration from Ops Agent collected logs.

[franciscovalentecastro]

Description

This test does the following :

• Create a test Instance Template and a Managed Instance Group (MIG).
• Creates a VM in the MIG that the test can SSH into.
• Register MIG to a test AppHub application ops-agent-app-hub-integration-test-app as a workload.
• Verify a custom syslog log contains the correct apphub.* labels in Cloud Logging.

Related issue

b/354756009

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
  • 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.