Panic when attempting to delete operators namespace

[difrost]

Description

An attempt to delete namespace where the Operator is running should trigger a panic() which will allow further tracing of such cases. This change is a consequence of #2912 though the actual fix for a linked issue will require another PR.

For PR author

• Tests for change.
• If changing pkg/apis/, run make gen-files
• If changing versions, run make gen-versions

For PR reviewers

A note for code reviewers - all pull requests must have the following:

• Milestone set according to targeted release.
• Appropriate labels:
  • kind/bug if this is a bugfix.
  • kind/enhancement if this is a a new feature.
  • enterprise if this PR applies to Calico Enterprise only.