Maintain finalizers that we don't own

[caseydavenport]

Description

Avoid the operator removing finalizers that it doesn't own.

Release Note

Fix that operator would remove other controllers finalizers from objects it creates.

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.