Added Support for Handling Medical Discharge

[IllianiCBT]

Updated Person class to include method for retrieving permanent injuries.

Modified Campaign to retire personnel with permanent injuries instead of sacking them, bypassing contract breaches. Adjusted RetirementDefectionTracker to provide the appropriate payout for medically discharged personnel. Medical Discharge occurs if the character resigns while possessing a permanent injury.

Fixed a bug in the payout logic that would cause personnel to always receive a 0 c-bill payout if they were sacked. Now the payout value correctly factors in whether the character is eligible for retirement or medical discharge.

Closes #4599

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 10.30%. Comparing base (dcbbd73) to head (6637f6f).
Report is 84 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4617      +/-   ##
============================================
- Coverage     10.30%   10.30%   -0.01%     
  Complexity     5822     5822              
============================================
  Files           936      936              
  Lines        129139   129148       +9     
  Branches      19000    19003       +3     
============================================
  Hits          13313    13313              
- Misses       114551   114560       +9     
  Partials       1275     1275              

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