Release strategy

My motivation to help working on the addon is to get rid of the annoying deprecations pointed out in #715
In the update process:
- #711
- #712
- #714
- #715

I figured out that it's not that simple to get it to work with ember `>=4` because the addon and probably the dependencies use the old ember imports and private apis that don't work anymore in ember 4.

That raises the question how we should release new versions to have a happy update path. The latest released version is `4.0.0-beta.12` which was released over a year ago. [NPM Versions](https://www.npmjs.com/package/ember-cp-validations) show that most downloads are for the beta releases.

My suggestion would be to release a version `4.0` that supports ember `<=3.28.x` and after that work on a new `5.0` release for ember `>=4`. That would allow us to drop support for ember `<=3.28.x` in the `5.x` branch and make things much easier.

We need to highlight [breaking changes](https://github.com/rwwagner90/ember-validators/blob/master/CHANGELOG.md#v400) from the `ember-validators` dependency.

I'm happy for more input and opinions.

- [x] Deprecate `volatile` option because `computed().volatile()` is removed:
- [x] https://github.com/emberjs/ember.js/pull/19670
- [x] https://github.com/adopted-ember-addons/ember-cp-validations/pull/718
- [x] Release `4.0.0-beta.13`
- [x] Fix ember `4.0` issues https://github.com/adopted-ember-addons/ember-cp-validations/pull/717
- [x] #720
- [x] Release `4.0` for ember `<=3.28.x`
- [x] Release `5.0` for ember `>=4`
- [x] Replace `ember-font-awesome` https://github.com/adopted-ember-addons/ember-cp-validations/pull/731
- [x] Update to ember-cli 4.8 https://github.com/adopted-ember-addons/ember-cp-validations/pull/732
- [ ] Update to ember-cli 4.12 https://github.com/adopted-ember-addons/ember-cp-validations/pull/736
- [ ] Replace `ember-data` imports https://github.com/adopted-ember-addons/ember-cp-validations/issues/740
- [ ] Enable `embroider-safe` and `embroider-optimized` scenarios https://github.com/adopted-ember-addons/ember-cp-validations/issues/739
- [ ] https://github.com/adopted-ember-addons/ember-cp-validations/issues/722