feat: Signer settings and CAWG signing

[redaranj]

Changes in this pull request

Adds support for creating a signer from JSON and TOML settings. Also adds support for CAWG signing via settings.

Intended to be merged after #16.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• All applicable changes have been documented
• Any TO DO items (or similar) have been entered as GitHub issues and the link to that issue has been included in a comment

[codecov]

Codecov Report

❌ Patch coverage is 53.84615% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.99%. Comparing base (c34508e) to head (d3c8cbf).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ary/src/main/kotlin/org/contentauth/c2pa/Signer.kt	50.00%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
+ Coverage   44.97%   44.99%   +0.01%     
==========================================
  Files          16       16              
  Lines         936      949      +13     
  Branches      130      135       +5     
==========================================
+ Hits          421      427       +6     
- Misses        442      446       +4     
- Partials       73       76       +3     

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