Make all alert policies optional

Summary

As part of our ongoing effort to centralise standard monitoring within the ucam-minimal-gcp-monitoring module, the alert policies defined in this module should be optional. While it is acceptable for the default behaviour to deploy these policies, we must ensure they can be disabled when required.

A separate issue in the ucam-minimal-gcp-monitoring project will re-implement these alert policies in line with our updated standards. In due course, gcp-deploy-boilerplate will be updated to use this module without deploying its built-in alert policies, as they will instead be managed through the ucam-minimal-gcp-monitoring module.

For now, this module will continue to configure the actual uptime check resources and supporting services, with no immediate plans to change that functionality.

Acceptance criteria

• All alert policies within this module can be optionally disabled, while the default behaviour remains to deploy them.