Releasing ARMI version 0.5.0

[john-science]

What is the change?

This is a simple version bump to ARMI version 0.5.0.

But I also:

• Did my usual pre-release cleanup of the release docs
• And I added some documentation of the new features.

Why is the change being made?

ARMI is getting close to a good point to release the next minor version. There has been a lot of work going on, and we are slowing our development phase, and moving into a testing phase.

---

Checklist

• [x] This PR has only one purpose or idea.
• [x] Tests have been added/updated to verify any new/changed code.

• [x] The code style follows good practices.
• [x] The commit message(s) follow good practices.

• [x] The release notes have been updated if necessary.
• [x] The documentation is still up-to-date in the doc folder.
• [x] The dependencies are still up-to-date in pyproject.toml.