[3.6] Remove the need of cdk arn class in PasswordSecretArnValidator

[eantonin]

Description of changes

• Remove the need of cdk arn class in PasswordSecretArnValidator

Tests

• The JUnit excercising that part were already present and they are still passing
• Launched 8 clusters with the custom resource, before the fix this would have almost surely showed at least an error, while it is not showing any error now, all validations succeeded

References

• The root cause is probably a race condition between the CDK import in PasswordSecretArnValidator and the one in the thread added in [3.x] Pre-import cdk libraries at the beginning of cluster create and update #4778 which runs in parallel with the validation.
• PasswordSecretArnValidator was the only validator importing cdk

Checklist

• Make sure you are pointing to the right branch and add a label in the PR title (i.e. 2.x vs 3.x)
• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

Please review the guidelines for contributing and Pull Request Instructions.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #5294 (47a7eb8) into release-3.6 (c8fac87) will increase coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           release-3.6    #5294   +/-   ##
============================================
  Coverage        89.74%   89.74%           
============================================
  Files              175      175           
  Lines            15256    15258    +2     
============================================
+ Hits             13692    13694    +2     
  Misses            1564     1564           

Flag	Coverage Δ
unittests	89.74% <ø> (+<0.01%)	⬆️

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see 1 file with indirect coverage changes

[enrico-usai]

Very great job finding the root cause of the issue, nice explanation!