Add error boundary wrapper type

[nightkr]

Motivation

Fixes #774. In short, bulk requests (like Api::list and watcher) are currently unable to cope with failing to parse individual objects, and instead treat the whole list as failed.

Solution

This PR introduces a new wrapper type DeserializeGuard<T>, which can be used instead of Api<T> to opt into a more lenient style, where the list parse succeeds but each object reports errors separately.

Since it implements Resource, it should also work transparently for APIs building on top of Api<T>, such as Controller<T>.

Ideally, it'd be nice if at least Controller<T> would use it transparently, but that would mean a breaking change on the Controller types to take the right Api variant.

[codecov]

Codecov Report

Attention: Patch coverage is 64.10256% with 14 lines in your changes missing coverage. Please review.

Project coverage is 75.4%. Comparing base (4af4d80) to head (5a7cefa).
Report is 1 commits behind head on main.

Files	Patch %	Lines
kube-core/src/error_boundary.rs	64.2%	14 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1556     +/-   ##
=======================================
- Coverage   75.6%   75.4%   -0.1%     
=======================================
  Files         79      80      +1     
  Lines       7237    7290     +53     
=======================================
+ Hits        5464    5495     +31     
- Misses      1773    1795     +22     

Files	Coverage Δ
kube-core/src/error_boundary.rs	64.2% <64.2%> (ø)

... and 8 files with indirect coverage changes

[clux]

This is very cool! Took me a while to grok this, but it's a very nice non-breaking way to inject an opt-in error in here. Left some suggestions and a few minor questions, but no major complaints.

[clux]

All good on my end.