Add ability to lock open threads

[jertel]

This PR addresses #45 by introducing three new optional parameters:

• include-issue-currently-open (default: false)
• include-pr-currently-open (default: false)
• include-discussion-currently-open (default: false)

I do not close discussions on my projects, and some discussions are not answerable. But I also do not want very old discussions to be commented upon. This PR provides the ability to auto lock those old, open discussions. For consistency, the issues and PRs are also capable of supporting this.

I have this actively running on two of my projects so far and it's working well. Example workflow:

name: 'Lock Threads'

on:
  schedule:
    - cron: '50 1 * * *'
  workflow_dispatch:

permissions:
  issues: write
  pull-requests: write
  discussions: write

concurrency:
  group: lock-threads

jobs:
  lock-threads:
    runs-on: ubuntu-latest
    steps:
      - uses: jertel/lock-threads@main
        with:
          include-discussion-currently-open: true
          discussion-inactive-days: 90
          issue-inactive-days: 30
          pr-inactive-days: 30

Feel free to close this if you prefer keeping the project to only work on closed threads.

Thanks for starting this project!