Add a service override environment variable

[aatauil]

Instead of specifying @queryManager({ service: 'apollo-override' }) apollo;everywhere, It might be interesting to have a service override environment variable as such:

apollo: {
  apiURL: '/graphql',
  overrideService: 'apollo-override'
  }

Seems an easy addition.

https://github.com/ember-graphql/ember-apollo-client/blob/99712f01a8918570a7a6455341d665602b7c70f7/addon/-private/apollo/query-manager.js#L27-L39

Could become this:

export function queryManager(...theArgs) {

  let setupQueryManager = computed(function () {

    let config = getOwner(this).resolveRegistration('config:environment');
    let serviceName = config.apollo.serviceOverride || 'apollo';
    let [options] = theArgs;
    if (typeof options === 'object' && options.service) {
      serviceName = options.service;
    }

    const service = getOwner(this).lookup(`service:${serviceName}`);
    const queryManager = new QueryManager(service);
    setupHooks(queryManager, this);
    return queryManager;
  });

the default apollo service would be used if no override service would be defined and you could still specify a completely different service instead by doing @queryManager({ service: 'apollo-special-case' }) apollo; for the edge cases.