fix(ember): resolve config path from app root

This should aid in resolving the app configuration from the right location.

Previously, it was calling `require` with a relative path from the `index.js` file of the Sentry addon itself. This broke trying to actually load the configuration file in _other_ apps or addons that might include this as a dependency.

The Ember addon API exposes the configuration path for a given app or addon through the `project.configPath()` method, which we can use instead to look up the location of the project's `config/environment.js` file.

Author: alexlafroscia

packages/ember/index.js

@@ -19,7 +19,7 @@ module.exports = {
   getAddonConfig(app) {
     let config = {};
     try {
-      config = require(app.options.configPath)(app.env);
+      config = require(app.project.configPath())(app.env);
     } catch(_) {
       // Config not found
     }