Split up create-release into "create tag" and "build release"

[JonnyOThan]

Currently, create-release does all the versioning work, commits a tag, AND builds the mod and creates a draft github release.

In many use cases we don't want the first part and only want to build a release from an existing tag. As a bonus, it shouldn't be hard to set up an automated workflow that runs whenever a tagged commit is pushed. So create-release should be split up - the part that sets up the final 'version bump" commit and tag, and then one that actually just builds the release from whatever is in the depot.