Allowed users to specify podModulePrefix (ember-app)

[ijlee2]

Description

Closes #1. If a user specified podModulePrefix in their config/environment.js, they can pass the argument --pod-path to the codemod. At the moment, the --pod-path argument affects only Ember apps.

Note, the name podPath came from the emberjs/ember.js repo. The value refers to the "difference" between podModulePrefix and modulePrefix. For example, if a user has the following config/environment.js:

/* config/environment.js */
'use strict';

module.exports = function (environment) {
  let ENV = {
    modulePrefix: 'my-app',
    podModulePrefix: 'my-app/pods',
    ...
  };

  return ENV;
};

then:

podPath = 'my-app/pods' - 'my-app' = 'pods'

So the user will need to enter the following command:

npx ember-codemod-pod-to-octane --pod-path=pods --type=app

Due to a change in APIs, this pull request unfortunately became large. There may be opportunities to refactor code. Let's do so in a separate issue and pull request.