gke-cluster-autopilot: add monitoring configuration

[olliefr]

Although one cannot disable Cloud Monitoring integration in GKE Autopilot clusters, one has some flexibility over which control plane components' metrics should be ingested: manage GKE metrics.

This PR adds a new input variable monitoring_config and a block to the cluster resource to facilitate that. The variable is optional with a sensible default value.

The interface is similar in style to #1625. Since there was no monitoring configuration in place for this module previously, it is not likely for this PR to break any existing code 🙏

I've added an example to the README as well.

Feedback is welcome 🙃

Checklist

If applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

[juliocc]

@olliefr thanks for this!

Does it make sense to have the same variable for standard clusters?

[olliefr]

@juliocc the standard cluster module already has it: monitoring_config.

Like the logging_config before, it's not an object interface though. My plan is to implement the object interface for the standard clusters module as well but I'd like to do it in a separate PR because the surface of work is much greater for the standard clusters - the configuration is more flexible for standard clusters and there are existing uses of the module, just like we had with logging.

[juliocc]

@juliocc the standard cluster module already has it: monitoring_config.

Like the logging_config before, it's not an object interface though. My plan is to implement the object interface for the standard clusters module as well but I'd like to do it in a separate PR because the surface of work is much greater for the standard clusters - the configuration is more flexible for standard clusters and there are existing uses of the module, just like we had with logging.

Sounds good. You can merge this one then.