Setup Embroider App - Githubissues

Copied and adapted from the ember-cli-mirage repo (to also test out if I really understand the migration process)

Extra changes (because there is a lot to sync up on)

ember-mirage is now an injected dependency
- this is the most accurate way to test how a dependency will behave when installed from npm
- see also: https://github.com/pnpm/pnpm/issues/4965
- docs: https://pnpm.io/package_json#dependenciesmetainjected
- I added the _syncPnpm script to make sure that the injected dependency stays in sync

Once this is merged, we could probably turn on renovate: https://github.com/bgantzler/ember-mirage/pull/10

bgantzler / ember-mirage