refactor: add command/release.bash

Adding command/release.bash which will tag multi-platform Docker images based on the image tagged with main. This should be automatic but the automated release pipeline has been failing. Theoretically command/release.bash should not be needed. But if the release job fails... well...

Assuming that the release pipeline (that runs when merging into main) has successfully created an image tagged with ":main" then command/release.bash can be used as follows. Assuming the new release version is 2.0.0

./commands/release.bash 2.0.0

Note that the person running this must have credentials sufficient for reading and writing the project's container registry on GitLab.