Add Appraisal

[natevick]

Add and setup Appraisal to run against multiple versions of Ruby/Rails/Minitest/RSpec. We should add this as a run in CI as well.

Here is an example of using Appraisal in GHA using workflow_dispatch. https://github.com/selectiveci/selective-ruby-rspec/blob/main/.github/workflows/test_all_the_things.yml