feat: translate only one if multiple KongVaults with the same spec.prefix

[randmonkey]

What this PR does / why we need it:

Translate only one of KongVaults and record translation failure events for the others if they have the same spec.prefix to avoid generating vaults with the same prefix in Kong configuration. The "winner" is chosen by the following rules:

• The one created earlier (earliest metadata.creationTimestamp)
• The one having name in smaller lexical order if the creation timestamp is the same.

And the PR also sets spec.prefix to be immutable.

Which issue this PR fixes:

fixes #5423

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

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

Comparison is base (785b0cb) 69.3% compared to head (694f63a) 69.5%.

Files	Patch %	Lines
internal/dataplane/kongstate/kongstate.go	90.3%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5435     +/-   ##
=======================================
+ Coverage   69.3%   69.5%   +0.1%     
=======================================
  Files        176     176             
  Lines      22386   22415     +29     
=======================================
+ Hits       15533   15579     +46     
+ Misses      5929    5916     -13     
+ Partials     924     920      -4     

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