GCP Marketplace integration for NGINX Ingress

[memes]

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Google Cloud's marketplace requires that the application report usage metrics periodically to GCP's service endpoint. UBB Agent SDK is used to send a count of 60 to the endpoint every 60 seconds, using credentials added as a secret during marketplace provisioning. If the secret is unavailable or invalid, ingress controller will terminate after five successive failures.

GCP Marketplace is click-to-deploy only; in addition to ingress controller, a deployer and tester container must be provided as a package.

This PR is related to issue #2859

Checklist

• [x] I have read the CONTRIBUTING doc
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked that all unit tests pass after adding my changes
• [x] I have updated necessary documentation
• [x] I have rebased my branch onto main
• [x] I will ensure my PR is targeting the main branch and pulling from my branch from my own fork