Automatically set an exact maxLength on enum fields in CRDs

[cbandy]

This automates what a CRD author would do anytime they add or change an enum field. See:

• Set OpenAPI maxLength on enum fields #4048

Checklist:

• Have you added an explanation of what your changes do and why you'd like them to be included?
• Have you updated or added documentation for the change, as applicable?
• Have you tested your changes on all related environments with successful results, as applicable?
  • Have you added automated tests?

Type of Changes:

• Other