Allow deploying to review environment from PR comments

[habbes]

Inside a PR comment, we should be able to do something to write a command like @deploy:review1 or /deploy review1 and it would push the PR to the review1 branch, which would trigger a build and deploy. Ideally, the command should only trigger or complete if it comes from someone with push access to the target branch.

It appears that there already some Github Action in the marketplace that can achieve this:

• https://github.com/marketplace/actions/slash-command-dispatch
• https://github.com/marketplace/actions/pull-request-comment-trigger