chore: publish docker image to GHCR; add helm chart

[invakid404]

This PR adds a GitHub Actions workflow which builds and publishes the Docker
image to GitHub's Docker image repository (GHCR), and adds a Helm chart for ease
of deployment in Kubernetes.

To get the GitHub Actions workflow up and running, two secrets need to be added
to the repository:

• GHCR_USERNAME: the username of the repository owner (in this case, trashhalo)
• GHCR_TOKEN: a GitHub personal access token which has the write:packages
  scope

The workflow runs when a new release is created and automatically builds and
tags a Docker image with both the tag name and latest.

For the Helm chart to be usable, an index.yaml file needs to be hosted
somewhere. For example, it can be hosted on GitHub Pages. Here's a
guide on how to create a Helm
chart repository.

Note that the Helm chart can only set the two environment variables that are
documented in the README. I noticed that there are other environment variables
in use throughout the codebase, but I'm not familiar with them. It could be
extended in the future with those as well.

[trashhalo]

Thanks for this pr. Ill take a deeper look at it this weekend