feat: Allow partial matches of allowed terms

[sarayourfriend]

Changes proposed

• Update the API of allowedTerms to be string|{ term: string, allowPartialMatches: boolean }
• Update rule logic to match partial terms when allowPartialMatches is true for an allowed term
• Update tests
• Fix a bug I found where the regex was matching parenthesis. See commit description for details and links to examples
• Refactor custom rule configuration parsing logic into a separate utils/custom-rule-config module
  • Just took a stab at an organization that made sense to me but happy to change it in any way if there are suggestions for how to make this better.

Fixes #6