Allow customization of assertion for outputunit

[justin-tay]

Closes #1030

This adds a constructor argument for OutputFormat.Hierarchical and OutputFormat.List to add a function to allow mapping of the ValidationMessage to an Object. This allows the message to be customized or allows the ValidationMessage to be passed through as is if the identity function is used.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.55172% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.18%. Comparing base (48ca3c2) to head (99d510a).
Report is 10 commits behind head on master.

Files	Patch %	Lines
...va/com/networknt/schema/output/OutputUnitData.java	80.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1033      +/-   ##
============================================
+ Coverage     78.90%   79.18%   +0.27%     
- Complexity     1965     1989      +24     
============================================
  Files           172      174       +2     
  Lines          6352     6437      +85     
  Branches       1255     1261       +6     
============================================
+ Hits           5012     5097      +85     
+ Misses          867      864       -3     
- Partials        473      476       +3     

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