Omit managed fields from cached Kubernetes objects

[cbandy]

Tests pass. This should reduce memory usage, but I haven't tried it in a large cluster, yet.

Checklist:

• [x] Have you added an explanation of what your changes do and why you'd like them to be included?
• [x] 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:

• [x] Other

Performance / Utilization

What is the new behavior (if this is a feature change)?

Reduced memory usage, TBD.

Other Information:

Issue: PGO-1362