Publish API docker image with multi-platform support

[djperrefort]

Add linux/amd64 and linux/arm64 at a minimum.

[djperrefort]

The CI pipeline for this project builds the docker image(s) at the beginning of each run and writes the result to GHA artifact storage for use in later CI stages. In regards to multi-platform builds, this raises a problem.

Docker supports saving containers/images to disk in various formats. As of right now, the default "docker" format does not support multi-platform builds, forcing us to switch to the OCI format instead. Unfortunately, docker uses it's "export" feature to write OCI images instead of it's "save" feature. The relevant difference here is that "export" creates a container snapshot and omits crucial metadata and build directives like CMD - all things we need to preserve in the published image.

After looking at related issues, we're not the only one's facing this problem. A common work around is to build the images separately and combine them later via a manifest. However, this gets messy to implement within our current CI architecture.

Here is a similar issue with a well thought out description: fiaas/fiaas-deploy-daemon#179

With all of this in mind, I'm marking this as "not planned" for now. I'm happy to revisit if/when docker makes things easier.

Ping @yassinkhalifa so he is aware.