Add backfill digest file validation for CloudTrail validate-logs

[IanLeeYT]

Issue #, if available:
N/A
Description of changes:
Update CloudTrail validate-logs cli to support backfill digest validation

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.41%. Comparing base (c4681b5) to head (d4f3cc0).
⚠️ Report is 99 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #10055      +/-   ##
===========================================
+ Coverage    93.39%   93.41%   +0.02%     
===========================================
  Files          210      210              
  Lines        17052    17127      +75     
===========================================
+ Hits         15925    15999      +74     
- Misses        1127     1128       +1     

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