Make ObjectMeta Non Exhaustive

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Currently the fields on ObjectMeta are public, making a breaking change to add additional metadata, such as in #2240

Describe the solution you'd like

I would like to make ObjectMeta non_exhaustive to allow adding new fields without requiring a breaking change.

This will require adding a constructor to ObjectMeta to allow it to be safely constructed outside of the crate.

Describe alternatives you've considered

Additional context

[tustvold]

Thinking about this a bit more, this is actually a feature, in that it forces implementations to consistently populate all the fields