Add support for v5 Exec protocol when using Kubernetes 1.29+

[jacobtomlinson]

With Kubernetes 1.29 we should be able to use the v5.channel.k8s.io exec protocol to close the stdin channel.

However, things don't seem to be working as expected with the latest kind 1.29 image and I'm getting 403 errors when connecting.

Pushing up a draft to see if the same thing happens in CI.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (673184d) 94.91% compared to head (fb11537) 94.64%.

Files	Patch %	Lines
kr8s/tests/test_objects.py	71.42%	2 Missing ⚠️
kr8s/_exec.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #270      +/-   ##
==========================================
- Coverage   94.91%   94.64%   -0.27%     
==========================================
  Files          27       27              
  Lines        2871     2878       +7     
==========================================
- Hits         2725     2724       -1     
- Misses        146      154       +8     

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