Avoid looking up API resources on APIObject.get() calls

[jacobtomlinson]

Now that #249 has implemented the ability to pass objects to kr8s.get() we can pass the cls in places like the APIObject.get() classmethod instead of passing the endpoint name.

One benefit of this is that we don't need to look up API resources to resolve the string back into a class again. This closes #251.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (aed0366) 94.56% compared to head (7b091f8) 94.56%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #252   +/-   ##
=======================================
  Coverage   94.56%   94.56%           
=======================================
  Files          27       27           
  Lines        2743     2743           
=======================================
  Hits         2594     2594           
  Misses        149      149           

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