Add integration tests for mutual ssl certificate chain validation

[SavinduDimal]

Purpose

• $Subject
• Related PRs: Add certificate chain validation to MutualSSLAuthenticator handler carbon-apimgt#12289
• Related Issues: Cannot use custom root CA with Mutual SSL and invoke APIs with a signed certificate api-manager#873

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 24.32%. Comparing base (93e2009) to head (2bb5a39).
Report is 7 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #13393      +/-   ##
============================================
+ Coverage     20.27%   24.32%   +4.04%     
- Complexity     1034     1243     +209     
============================================
  Files           254      254              
  Lines         11495    11495              
  Branches       1200     1200              
============================================
+ Hits           2331     2796     +465     
+ Misses         9135     8672     -463     
+ Partials         29       27       -2     

Flag	Coverage Δ
integration_tests	24.32% <ø> (+4.04%)	⬆️

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