[CI] Do not use branch names when publishing container images

[kurtismullins]

Description of Changes

Removes the creation of Docker Container Images with branch names as tags.

AMD/Intel Image Build

ARM Image Build

Both images merged into a multi-platform image

The created images in Dockerhub

Side Note: It is much nicer to cross-reference related/identical images in Github's Artifact Repository than it is in Dockerhub. Perhaps we should consider only using Dockerhub for spacetimedb:latest and tagged releases?

API and ABI breaking changes

n/a

Expected complexity level and risk

1

This complexity rating applies not only to the complexity apparent in the diff, but also to its interactions with existing and future code.

n/a

Testing

• See the included screenshots. I created tags which matched the blob pattern v* and verified that the tag names are correct by looking at the CI output and cross-referencing DockerHub.