Add --ignore-unsupported-specs flag to validate command

[makavity]

Closes #831

[codecov-commenter]

Codecov Report

❌ Patch coverage is 4.16667% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 31.25%. Comparing base (8a3be4f) to head (6b94291).

Files with missing lines	Patch %	Lines
cmd/sloth/commands/validate.go	0.00%	23 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #832      +/-   ##
==========================================
- Coverage   31.30%   31.25%   -0.05%     
==========================================
  Files         149      149              
  Lines        9228     9236       +8     
==========================================
- Hits         2889     2887       -2     
- Misses       6088     6097       +9     
- Partials      251      252       +1     

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