Improve flexibility when getting resources by name

[jacobtomlinson]

Closes #196

This PR makes many general improvements to kr8s._objects.get_class to enable looking up classes from various strings. Previously this had only been implemented inkubectl-ng so this PR pushes that down into kr8s and also adds more flexibility.

The outcome is that when using kr8s.get(resource) the resource now supports the formats KIND[.GROUP][/VERSION] or KIND[.VERSION][.GROUP] where KIND can be singular, plural, titlecase or a short name.

Examples

import kr8s

pods = kr8s.get("pods")  # Only this worked previously
pods = kr8s.get("pod")  # Singular
pods = kr8s.get("Pod")  # Title
pods = kr8s.get("po")  # Short name
pods = kr8s.get("pods/v1")  # Explicit version

For resources that have an API group such as roles.rbac.authorization.k8s.io/v1 we can also select that in various ways.

import kr8s

roles = kr8s.get("roles")  # Only this worked previously
roles = kr8s.get("role")  # Singular
roles = kr8s.get("Role")  # Title
roles = kr8s.get("roles.rbac.authorization.k8s.io")  # Full group name
roles = kr8s.get("roles.rbac.authorization.k8s.io/v1")  # Full group name with explicit version
roles = kr8s.get("roles.v1.rbac.authorization.k8s.io")  # Full group name with explicit version alternative

[codecov]

Codecov Report

Merging #198 (f939436) into main (f94a526) will increase coverage by 0.04%.
The diff coverage is 97.82%.

@@            Coverage Diff             @@
##             main     #198      +/-   ##
==========================================
+ Coverage   94.96%   95.01%   +0.04%     
==========================================
  Files          25       25              
  Lines        2405     2448      +43     
==========================================
+ Hits         2284     2326      +42     
- Misses        121      122       +1     

Files	Coverage Δ
kr8s/_api.py	90.68% <100.00%> (+0.23%)	⬆️
kr8s/tests/test_api.py	100.00% <100.00%> (ø)
kr8s/tests/test_objects.py	98.78% <100.00%> (+0.01%)	⬆️
kr8s/_objects.py	92.12% <95.45%> (+0.08%)	⬆️