Fix ESLint setup

[raucao]

babel-eslint isn't working with node 16 anymore.

In addition to the new packages, also turn the remaining Ember errors into warnings, so we can fix them without npm test failing in the meantime.

[raucao]

You can easily verify the config by running npm test on your machine and checking that there are no errors and the command exits without an error code, too.

[bumi]

I had ran it, got no errors just "classic classes" warnings.