Validate LicenseToken field is not used by other clusters

[panktishah26]

Issue #, if available:
#6793

Description of changes:
Validate the license token is not being used by multiple clusters for extended kubernetes version support for eks-a controller.

Testing (if applicable):

Documentation added/planned (if applicable):

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[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 72.32%. Comparing base (21b4f95) to head (aa8aa67).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/validations/extendedversion.go	60.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9222   +/-   ##
=======================================
  Coverage   72.31%   72.32%           
=======================================
  Files         587      587           
  Lines       46056    46081   +25     
=======================================
+ Hits        33306    33328   +22     
- Misses      11000    11003    +3     
  Partials     1750     1750           

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