Replace ember-ajax with ember-fetch for Octane

[betocantu93]

Ember octane blueprint comes without jquery, so ember-ajax is no longer needed. One option is to use ember-fetch instead.

Currently to use ember-fetch with ember-data, you have to use the AdapterFetch mixin from ember-fetch.

   //src/data/models/application/adapter.js

   import DS from 'ember-data';
   const { Adapter } = DS;
   import AdapterFetch from 'ember-fetch/mixins/adapter-fetch';

   const AdapterWithFetch = Adapter.extend(AdapterFetch);

   export default class ApplicationAdapter extends AdapterWithFetch {

   }