Await overriden functions when returning promises

[ghusse]

According to ember's documentation, the function beforeModel on routes can return Promises.

The previous implementation of ember-apollo-client did not allow to correctly use both async beforeModel & @queryManager on a route. Because of the override done by the plugin, it was not possible to await for the result of a beforeModel method.

With this fix,

• when a hooked function returns a Promise, a promise is returned by the hooked function, allowing to wait for its completion.
• when a hooked function does not return a Promise, it works as before.

[Thenkei]

• ✅ Code review
• ✅ Automatic tests
• ✅ Manual tests
• ❔  PR title - I don't know the convention naming used

[josemarluedke]

Thank you @ghusse . Published in v4.1.0.

[ghusse]

Thanks!