Add GitHub Actions workflow to trigger deployment on master updates

[pedrogaudencio]

Problem

We want deployments to happen when a PR is merged into master, and we want a workflow where GitHub only triggers a server-side deploy script (the VM builds + pushes to local registry + runs by digest).

Solution

Add a GitHub Actions workflow triggered on push to master that only ssh’s into the VM and runs a restricted deploy command.

Notes: following up /issues/111