Ember 4.0 compatibility - drops support for Ember < 3.28

[fsmanuel]

Breaking changes:

• Drop support for Ember < 3.28

First attempt to make it ember 4.0 compatible.

• [x] Remove volatile() from the code base
• [x] https://github.com/qonto/ember-cp-validations/pull/13

Thanks to @zeppelin and @qonto I could cherry pick a lot from the fork.

ref #716 closes #701

[fsmanuel]

@tehhowch wanna do another review?

[tehhowch]

@fsmanuel i was able to pull this down and run unit & integration tests for some just-migrated-to-3.28 apps, without issues. We have more extensive test suites but they are more costly to run, so they'll need to wait until this PR is released in 5.0

I'm curious: does this PR drop support for Ember 3.24 just because, or are there things only in 3.28 or later that are necessary for the current implementation?

[kiwi-josh]

As another data point (as someone running a large ember app in production on the https://github.com/qonto/ember-cp-validations/commit/3767e4114e0c327138287486094e228bd71a45ec fork). I pointed our repo at this PR, smoke tested a bunch of validation functionality, and ran our test suite, and all green 😄

[fsmanuel]

@MelSumner thanks for approving! @tehhowch @kiwi-josh thanks for testing with a real app.

@tehhowch I think I needed to drop support for 3.24 but I'm not 100% sure. The general problem with old versions is that the maintaining efforts for the test coverage increases a lot. For example ember bootstrap was used in this addon for the docs and then you need to figure out which ember, addon and ember bootstrap versions work well together. Because ember 4 is significantly different it's best to drop the test coverage for the old versions to make life easier with the upcoming changes to this addon.

[fsmanuel]

Released as 5.0