Add IP pool config to disable new allocations

[caseydavenport]

Description

Add new operator API field to IP pools that is equivalent to the exisitng IP pool spec.disabled option.

This is necessary if we want to implement IP pool migration logic from this guide using the operator API: https://docs.tigera.io/calico/3.27/networking/ipam/migrate-pools#tutorial

Separately, I do wonder if we could make pool migraiton even easier in operator mode - could the operator automatically do most of those steps?

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.