Remove use of deprecated pod phase

[Sovietaced]

Why are the changes needed?

v1.PodUnknown has been deprecated and unused since 2015. My IDE has warning messages and I figured it should be safe to just cleanup this part of the code.

See: https://pkg.go.dev/k8s.io/api/core/[email protected]#PodUnknown

What changes were proposed in this pull request?

Removes all references to v1.PodUnknown pod phase.

How was this patch tested?

Unit tests

Setup process

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

Docs link

Summary by Bito

This pull request removes all references to the deprecated pod phase `v1.PodUnknown`, which has been unused since 2015. The updates across multiple files enhance code cleanliness and maintain functionality. Unit tests were added to ensure existing features remain intact.

[flyte-bot]

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.58%. Comparing base (6e343cd) to head (c13de65).
⚠️ Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
flyteplugins/go/tasks/plugins/k8s/pod/plugin.go	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6640      +/-   ##
==========================================
- Coverage   59.92%   58.58%   -1.35%     
==========================================
  Files         708      929     +221     
  Lines       51365    70906   +19541     
==========================================
+ Hits        30783    41541   +10758     
- Misses      18270    26212    +7942     
- Partials     2312     3153     +841     

Flag	Coverage Δ
unittests-datacatalog	59.03% <ø> (ø)
unittests-flyteadmin	56.13% <ø> (ø)
unittests-flytecopilot	40.87% <ø> (ø)
unittests-flytectl	64.64% <ø> (ø)
unittests-flyteidl	76.12% <ø> (ø)
unittests-flyteplugins	61.09% <50.00%> (-0.01%)	⬇️
unittests-flytepropeller	55.06% <ø> (?)
unittests-flytestdlib	63.03% <ø> (-0.02%)	⬇️

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[machichima]

LGTM. Thanks!