Support multiple Rails versions?

[ryanfb]

Right now we only support Rails 6.1. It would be nice to be able to support multiple versions of Rails and load version-appropriate patches automatically.

[ryanfb]

Some good info here:

• http://greena13.github.io/blog/2020/12/19/writing-ruby-gems-for-different-versions-of-ruby-and-rails/
• https://stackoverflow.com/questions/27389678/how-to-test-a-rails-engine-which-should-support-both-rails-3-and-rails-4