[MESH-5515] Add 'security.istio.io/tlsMode' label to SE endpoints for deployment to rollout migration usecase

[Punakshi]

• Updated various test cases to include the 'security.istio.io/tlsMode' label in Service Entries and Workload Entries.
• Modified validation logic to check for the presence of the 'security.istio.io/tlsMode' label.
• Refactored code to ensure the 'security.istio.io/tlsMode' label is added where necessary.
• Enhanced error handling in validation functions to provide detailed error messages.

Checklist

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• I updated unit and integration tests (if applicable).
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Description

What does this change do and why?

[Link to related ISSUE]

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Codecov Report

Attention: Patch coverage is 73.68421% with 5 lines in your changes missing coverage. Please review.

Project coverage is 71.72%. Comparing base (4b33279) to head (eb9ceec).

Files with missing lines	Patch %	Lines
admiral/pkg/clusters/serviceentry.go	76.92%	2 Missing and 1 partial ⚠️
admiral/pkg/clusters/configwriter.go	33.33%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #343      +/-   ##
==========================================
- Coverage   71.72%   71.72%   -0.01%     
==========================================
  Files          66       66              
  Lines        9241     9248       +7     
==========================================
+ Hits         6628     6633       +5     
- Misses       2254     2255       +1     
- Partials      359      360       +1     

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