Overlay module improvements

[cppforlife]

Desired improvements around Overlays.

This Epic is a kind of scratch pad of ideas.

When one becomes pertinent:

1. create a story (attached to this epic) based on a to-do (from the "Ideas" section).
   • take a hard look at the "notes from the plane" gist, there's likely some good hints in there.
   • chat with @cppforlife for additional context
2. delete that "to-do" from this list.

Ideas

Specific improvements to consider.

• [ ] #371
• [ ] @overlay/append should not require a corresponding @overlay/match
  • #carvel shows an example
• [ ] match child defaults needs to better merge if node specific rules
  • node specific rules should take precedence
  • this ends up to be if any missing_ok/expects/when is specified on node, we should throw away defaults for that node
• [ ] rename expects to expect kwarg?
• [ ] docs: add table to docs describing overlay actions behaviors
• [x] vmware-tanzu/carvel#112 — how to add overlay annotation on a first map item within an array item
• [x] #116
  • improved: https://github.com/cloudfoundry/cf-for-k8s/blob/6c9f5cd30acbfe0644bc323da73444b9c41e4617/config-optional/remove-resource-requirements.yml -> https://gist.github.com/cppforlife/7a5f061a184e09a33f2cab2ee433795c

notes from the plane: https://gist.github.com/cppforlife/f5eddb3f7dd73239144fb0c148d8f9f2

Previously Completed

Kept for historical purposes: improvements that were made before this issue was converted to an Epic.

• [x] change default array match matcher to not_op(all) which would result in appending?

[cppforlife]

when= included in https://github.com/k14s/ytt/releases/tag/v0.28.0