Attach to Trello Card action

The purpose of this action is to enable attaching a pull request to Trello cards, from within the PR body. This is best used with the Trello Github Power-Up added to your Trello Boards. With that enabled, this effectively enables the "Attach Pull Request" action of the Power-Up, but from the Github side (and via a quick URL copy-paste instead of clicking through menus).

The action looks for Trello card URLs at the start of a Pull Request description. If found, it will add the PR URL as an attachment to each specified card in Trello.

Optionally, this can be configured to also attach (redundant) PR comments with card links/names, similar to what the Trello Power-up will do, for use cases requiring that.

Link-Finding

URLs need to each be on own line (leading/trailing whitespace and extra blank lines don't matter), and be at top of PR body. URLs embedded in other text are ignored, as are URLs after descriptive (i.e., non-link) text starts. Both the short-form (from the "Link to this card" field provided by a card's "Share" button) or long-form (cmd/ctrl+c with card open, copy from url bar with card open, etc.) are supported.

So, for :

https://trello.com/c/aaaaaaaa

https://trello.com/c/bbbbbbbbb/111-qqqqqqqqqqqq
This PR impl's the above 2 features.  These work similarly to feature https://trello.com/c/ccccccccc.  
The below is a random trello url put in this body, for some reason:
https://trello.com/c/dddddddd

only cards aaaaaaaa and bbbbbbbbb will have the PR attached.

Events

Workflows using this action should include some/all of the following supported event types:

• pull_request.opened
• pull_request.reopened
• pull_request.edited

Unsupported actions are ignored.

Inputs/Outputs

This requires Trello key and token to be supplied from the workflow where used. The token, at least, should come from repo Secrets.

There are no outputs.

Example workflow config:

name: Attach to Trello
on:
  pull_request:
    types: [opened, reopened, edited]
jobs:
  attach-trello:
    runs-on: ubuntu-latest
    name: Find trello link and attach to card
    steps:
      - uses: delivered/attach-to-trello-card-action@master
        with:
          trello-key: ${{ secrets.TRELLO_KEY }}
          trello-token: ${{ secrets.TRELLO_TOKEN }}
          
          ## optional
          # add-pr-comment: true
          ## required if add-pr-comment is true.  secrets.GITHUB_TOKEN is supplied by GH action implicitly.
          # repo-token: ${{ secrets.GITHUB_TOKEN }}

Development Notes

Incrementing version

1. Update version in package.json (format should be X.X.X, per semver)
2. Commit/push changes
3. Create release (and publish to marketplace) - use 'v'-prepended format for new tag and release name