Add priorityClassName in PropagationPolicy & ClusterPropagationPolicy

[seanlaii]

What type of PR is this?
/kind api-change
/kind feature

What this PR does / why we need it:
Add PriorityClassName to PropagationPolicy & ClusterPropagationPolicy.

Which issue(s) this PR fixes:
Part of #5961

Special notes for your reviewer:

• The PriorityClassName field follows the same pattern as Kubernetes PodSpec.PriorityClassName
• Falls back to global default PriorityClass if unspecified, similar to Pod priority behavior
• Implementation preserves backward compatibility as the field is optional

Does this PR introduce a user-facing change?:

Add PriorityClassName field to PropagationPolicy and ClusterPropagationPolicy, allowing users to specify priority and preemption behavior through PriorityClass objects. This provides more flexible and standardized priority management for resource propagation.

[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.18%. Comparing base (8d89d77) to head (2d81d50).

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5962   +/-   ##
=======================================
  Coverage   48.17%   48.18%           
=======================================
  Files         664      664           
  Lines       54799    54799           
=======================================
+ Hits        26399    26403    +4     
+ Misses      26684    26681    -3     
+ Partials     1716     1715    -1     

Flag	Coverage Δ
unittests	48.18% <ø> (+<0.01%)	⬆️

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