Change dependency from annotate to annotaterb

[drwl]

This PR changes the project to use AnnotateRb instead of Annotate.

I tested it locally and there are no changes to the annotation configuration nor annotations themselves. What does change is the CLI, so if running annotations manually previously you would use bundle exec annotate, now one would use bundle exec annotaterb models.

I was a maintainer of the old gem (annotate) but decided last year to make a fork and tidy up the code a lot. The new gem (annotaterb) is actively maintained and should perform faster for newer Rails (6+) apps because it leverages Zeitwerk instead of eager loading everything.

This PR is self-serving in that it does grow usage of my project, so feel free to reject this. I am also happy to answer any questions.