MirageJS as peer dependency

[cah-brian-gantzler]

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This makes MirageJS a peer dependency. This is a breaking change. Any existing applications using ember-cli-mirage will have to rerun the default blueprint ember install ember-cli-mirage or add miragejs to your package.json mannually.

Fixes: https://github.com/miragejs/ember-cli-mirage/issues/2416

[cah-brian-gantzler]

Would you be opposed to adding Husky. I have it on my own apps so keep forgetting to run lint and prettier prior to submitting PRs :)

[ef4]

This is a good change, without it people cannot reliably adopt the new pattern that is documented for 3.0 (importing directly from miragejs).