Updates instructions around patching, for incident management

Addresses the feedback in gitlab-com/gl-infra/delivery#1386 (closed) to include Kubernetes clusters and is more specific about what can be patched.

This change is part of a group MRs that improve how we handle patching for k8s given the introduction of gitlab-shell

• Add more debug to show how variables are set gitlab-com/gl-infra/k8s-workloads/common!82 (merged)
• Patcher will set POST_DEPLOYMENT_PATCH=true when it does the k8s trigger https://ops.gitlab.net/gitlab-com/engineering/patcher/-/merge_requests/46
• Skip image checks when POST_DEPLOYMENT_PATCH is set to true and ensure it is clear that IMAGE_CHECK_OVERRIDE needs to be set to true gitlab-com/gl-infra/k8s-workloads/gitlab-com!564 (merged)
• Updates incident handling instructions and add the new POST_DEPLOYMENT_PATCH to variable list !307 (merged)