Add GitHub workflow file to build/tag/push custom docker images

[Exairnous]

This allows docker images with a custom tag/name to be created on demand for any branch containing this workflow and pushed to the specified docker repository. Two versions of the docker image will always be pushed, one ending with -latest and one ending with the workflow run number, e.g. my-custom-image-name-latest and my-custom-image-name-42.

This should help make it easier to customize Community Edition instances, test pull requests/development branches, and to provide docker images of long running branches (large alpha/beta features) for community testing.

Once this is finalized, it will be added to the other repositories that can benefit from it as well.

[Exairnous]

I'm not sure where the documentation for this workflow should live (the wiki for each repository, the hubs-docs repo, somewhere else?), so for now I'm just going to post it here in this comment:

Building Custom Docker Images

In each repository there is a GitHub Workflow/Action named custom-docker-build-push for building custom docker images and pushing them to a docker/container registry of your choice. Simply run this Action on any branch, with the appropriate details filled in (either through the predefined defaults or by the overrides), and you will end up with a docker image of that branch that can be used in any Community Edition instance.

The Action allows you almost complete control over where your docker images are sent and how they are tagged. The details required for this to work can either be provided at runtime or by preset defaults that you set up.

Options/Setup

The following properties can be configured/overridden. Any values that are manually specified for that run will always be used. Any fields not passed values will fall back on predefined variables/secrets (if they have been created).

Options:

• The branch the workflow will run on. [REQUIRED]
  • This has to be manually specified each time when running the Action.
• The registry base URL. [REQUIRED]
  • This is used to specify which docker/container registry to push to.
  • Common values include: docker.io for Docker Hub, and ghcr.io for GitHub. For other registries, check their documentation on what to put here.
  • Create a repository variable named REGISTRY_BASE_URL to set a default registry to use.
• The registry username. [REQUIRED]
  • The username of the account for the registry you want to push to.
  • Create a repository secret named REGISTRY_USERNAME to set a default username to use.
• The registry password. [REQUIRED]
  • The password of the account for the registry you want to push to.
  • Create a repository secret named REGISTRY_PASSWORD to set a default password to use.
• The registry namespace. [REQUIRED]
  • This is often the same as the username, but some registries allow you to manually specify a namespace.
  • Create a repository variable named REGISTRY_NAMESPACE to set a default namespace to use.
• The image tag. [OPTIONAL]
  • This is basically the name of your image.
  • The default value of this is the branch name.
  • When the workflow is run, two images/tags will be pushed to the registry, one will be the <image_tag_value>-latest and the other will be the <image_tag_value>-<action_run_number>, e.g. my-cool-branch-latest and my-cool-branch-42
• The name of the Dockerfile [OPTIONAL]
  • This has been preset and you shouldn't need to change it unless you've changed the name/location of the Dockerfile in your code. If you have changed the name/location of your Dockerfile you will need to specify this each and every time you run the Action or update the default in the GitHub workflow file.
• The code path. [OPTIONAL]
  • The path to the code you want built. Used for only building a specific part of the repo.
  • This doesn't usually need to be filled/changed.
• The build cache.
  • Using the build cache will speed up subsequent builds of your images, but can sometimes cause problems with registries.
  • This is enabled by default, but if you run into problems building, you can disable it. The build will be slower, but it should hopefully work.
  • Example error to watch out for: buildx failed with: ERROR: failed to solve: error writing manifest blob: failed commit on ref "sha256:xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx": unexpected status from PUT request to https://xx.xxxxxxx.xxx/xx/namespace/repository/manifests/buildcache: 400

[Exairnous]

@mikemorran I've credited Brandon Patterson as mentioned here: https://github.com/Hubs-Foundation/hubs-blender-files/blob/main/creator-labs-files/CL-archive/ghost-to-md-output/2023-10-16-community-edition-case-study-quick-start-on-gcp-w-aws-services.md, but should I be crediting you as well? Also, I see there are two steps for the docker/setup-buildx-action, do you know if there is a reason for this? As far as I can tell, having duplicate build steps doesn't cause any problems, but I'd like to either remove one or add a comment explaining why there are two.