Implement CI for MystBin

[AbstractUmbra]

Description

This PR adds capability for CI for MystBin using GitHub actions.

The steps it follows are:-

1. A push to main will build a Docker image of the MystBin software and publish this to GHCR under the PythonistaGuild organization. This will be a public image so that anyone may use it.
2. On a successful build and publish of this image, it will execute a deployment action and deploy this newly built image to the current host of MystBin.
   2a) This deployment stage will only restart the mystbin service, not the pg database nor the redis cache.

This is currently not very testable due to the limitations of GitHub actions and may require subsequent PRs. In such cases I will use my break-glass privileges to squash and force push any fixes I must do.

Non-goals of this PR:-

• HADR / Replication of the database for a staging environment.
  • I plan to tackle this at a later date.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
  • I have updated the changelog with a quick recap of my changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)
• I have read and agree to the Developer Certificate of Origin for this contribution