Support GCP Marketplace deployment of NGINX+ ingress controller

[memes]

As a customer, I want to purchase NGINX+ ingress controller through pay-as-you-go deployments in GKE, including variants for App Protect, App Protect DoS, and combinations of the two.

Tagging @brianehlert for review.

PR #2860 includes the following:

• A billing agent is included in builds tagged with gcp that retrieves a secret containing billing credentials created as part of GCP's deployment process
• Patched helm charts to support passing GCP specific params to the container
• GCP marketplace deployer and apptest helm charts used to install and test deployments
• Dockerfiles and supporting files for the deployer and apptest container images
• Documentation/example

[github-actions]

Hi @memes thanks for reporting!

Be sure to check out the docs while you wait for a human to take a look at this 🙂

Cheers!

[memes]

@lucacome I have made changes to the proposed PR to support embedding the product identifier during build and to pass the GCP Marketplace usage-reporting secret via environment variable at run-time. Branch has been rebased onto main and squashed, please review #2860.

I created a separate repo for required GCP Marketplace deployer and apptest at https://github.com/memes/kubernetes-ingress-gcp-mp - lmk about transferring repo to nginxinc org.

[pdabelf5]

NGINX Ingress Controller is now available on the GCP Marketplace