feat: add action.yml for github action support

[jpbruinsslot]

Description

This PR introduces action.yml to enable alert2issue to be used as a github action.

Changes

• Added a version input that defaults to local, this ensures that the action installs the bundled code within the repository's current tag.
• Users can also use a pinned version (e.g. uses: annejan/alert2issue@v0.2.0) when they need a particular pypi version.
• Added configurable inputs:
  • repo_file: path to the list of repositories to scan
  • dry_run: toggle to preview actions without creating issues
  • min_rate_limit: safety check to prevent api exhuastion
  • gh_token: support for both GITHUB_TOKEN and PATs

Usage

With a repos.txt, one repo per line:

- name: Sync Dependabot Alerts to Issues
  uses: annejan/alert2issue@v1
  with:
    repo_file: 'my_repos.txt'
    gh_token: ${{ secrets.PAT_TOKEN }}

Or without, defaults to current repo:

- name: Sync Dependabot Alerts to Issues
  uses: annejan/alert2issue@v1
  with:
    gh_token: ${{ secrets.GITHUB_TOKEN }}