Add appraisal to test different `activesupport` versions

[RenzoMinelli]

Summary

• Add appraisal to use different versions of activesupport
• Add appraisal in CI, excluding failing cases

Why?

This will instill more confidence when making code changes by ensuring our code's compatibility with different activesupport versions

[mLewisLogic]

Thanks for this. Mind adding a section in the README to describe how to run appraisal and update the Appraisal specs in the future?

[mLewisLogic]

Thank you! Haven't worked on this project in a long time. Glad you're finding it useful.