Add PNG optimization workflow

[czyzby]

---

name: Pull Request
about: GitHub Actions setup
title: 'Add PNG optimization workflow'
labels: 'enhancement'
assignees: 'knyghtmare'

---

Describe your pull request does

This PR adds automatic workflow that optimizes and commits images to the master branch after every push.

[knyghtmare]

added the secret key from my end

[czyzby]

@knyghtmare Seems like it doesn't bypass the protected branch check after all. Other than adding the secret, are you sure the public key was added as a deploy key? Maybe you could also check the branch protection settings and see if you can enable direct commits with the deploy keys. If that ends up being a dead end, the only other way we could solve this is by opening PRs after each push, but that might increase the maintenance on your end a bit. Feel free to remove the workflow if ImgBot does that without all the hassle.