feat: Add support for vanity URLs

[ianlewis]

Description:

Adds support for matching vanity urls in actions/issue-reopener. Vanity URLs can be defined in a .todos.yml located in the repository root.

Related Issues:

Fixes #100

Checklist:

• Review the CONTRIBUTING.md documentation.
• Add a reference to a related issue in the repository.
• Add a description of the changes proposed in the pull request.
• Add unit tests if applicable.
• Update documentation if applicable.
• Add a note in the CHANGELOG.md if applicable.
• Sign the Google CLA.

[codecov]

Codecov Report

Merging #1017 (ee54c67) into main (3c12e3f) will increase coverage by 0.47%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1017      +/-   ##
==========================================
+ Coverage   81.61%   82.09%   +0.47%     
==========================================
  Files          18       19       +1     
  Lines        1050     1078      +28     
  Branches       14       17       +3     
==========================================
+ Hits          857      885      +28     
  Misses        140      140              
  Partials       53       53              

Files	Coverage Δ
actions/issue-reopener/src/action.ts	92.85% <100.00%> (+1.94%)	⬆️
actions/issue-reopener/src/config.ts	100.00% <100.00%> (ø)
actions/issue-reopener/src/reopener.ts	100.00% <100.00%> (ø)