Stabilise runtime predicates

[clux]

These are unlikely to undergo much changes (and they are basically a completely separate part in the codebase). This should be an easy feature cleanup in runtime, and one less need for unstable-runtime for common setups (i use this all the time).

This removes the kube_runtime/unstable-runtime-predicates feature and thus removes the need for users to use kube/unstable-runtime if they only are using predicates.

Public api wise; this exposes the Predicate trait, the WatchStreamExt::predicate_filter fn, and by necessity the (unconstructible) PredicateFilter stream wrapper type.

(Not planning on merging until near the release cycle in case any more fixes come in).
Idea via kube-rs/controller-rs#50 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.2%. Comparing base (6688421) to head (9cdf619).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1578   +/-   ##
=====================================
  Coverage   75.2%   75.2%           
=====================================
  Files         82      82           
  Lines       7334    7334           
=====================================
  Hits        5514    5514           
  Misses      1820    1820           

Files with missing lines	Coverage Δ
kube-runtime/src/utils/mod.rs	62.3% <ø> (ø)
kube-runtime/src/utils/watch_ext.rs	22.3% <ø> (ø)

[mateiidavid]

LGTM 👍🏻 seems like a sensible thing to do.