Update CI and CD

[alexevanczuk]

This updates CI and CD based on explorations in use_packwerk. Here are the several changes:

1. The biggest change here is that the publish step is now CD – that is, publishing happens automatically. Once a commit lands on master, it is tagged with the version of the gem ( no action is taken if a tag already exists), that tag is pushed to git, and then the gem is built and pushed to rubygems. Then a release is automatically created with autogenerated r elease notes.
2. I bump the version of a handful of thse actions, which gets rid of some deprecation warnings and adds some new features
3. I switch to using the bundle cache for setup-ruby, which speeds things up and also drops some boiler plate from other actions in CI
4. I update the naming on some of the steps so it's more readable and also consistent across rubyatscale repos.
5. I change CI to happen on push, which is seemingly a superset of pull_request, so now we need to run half as many actions, cutting our usage down and also removing unnecessary noise.

I think that's all!