Determine better strategy for handling map merging for various fields

[jaronoff97]

Right now we have to manually clear maps for only the node selector in the mutate.go, but i'm sure there are other places where we shouldn't blindly merge things together.

Originally posted by @swiatekm-sumo in #2941 (review)

[swiatekm-sumo]

In reality, I think the logic here should be very simple. We should clear everything except labels and annotations, and even in their case I'm not completely convinced this is a good idea. It's another question whether this is actually straightforward to do with our current tooling.

[jaronoff97]

Yeah maybe this is worth doing for everything... if anyone reading this wants to check it out do reach out!