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_ addons that might
include this as a dependency.

By resolving the config path relative to the app root first, we can
correctly load the file even when `@sentry/ember` is used within another
addon.

Author: alexlafroscia

packages/ember/index.js

@@ -1,5 +1,6 @@
 'use strict';
 const fs = require('fs');
+const { resolve } = require('path');
 
 function readSnippet(fileName) {
   return `<script>${fs.readFileSync(`${__dirname}/vendor/${fileName}`, 'utf8')}</script>`;
@@ -19,7 +20,8 @@ module.exports = {
   getAddonConfig(app) {
     let config = {};
     try {
-      config = require(app.options.configPath)(app.env);
+      const fullConfigPath = resolve(app.project.root, app.options.configPath);
+      config = require(fullConfigPath)(app.env);
     } catch(_) {
       // Config not found
     }