chore: Clean up unused files, imports, and work on getting end-to-end tests and unit tests running (#2272)

docs/v2/extensions/lifecycle/pre-registration.md

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+# Lifecylce Hook: preRegistration
+
+If an extension defines the `preRegistration` lifecycle hook, it is called
+before any modules are registered in the `ExtensionManager`. This hook can be
+used to:
+
+- initialize 3rd party libraries
+- register event listeners
+- add or call services
+- add or call commands
+
+The `preRegistration` hook receives an object containing the
+`ExtensionManager`'s associated `ServicesManager`, `CommandsManager`, and any
+`configuration` that was provided with the extension at time of registration.
+
+_Example `preRegistration` hook implementation_
+
+```js
+export default {
+  id: 'MyExampleExtension',
+
+  /**
+   * @param {object} params
+   * @param {object} params.configuration
+   * @param {ServicesManager} params.servicesManager
+   * @param {CommandsManager} params.commandsManager
+   * @returns void
+   */
+  preRegistration({ servicesManager, commandsManager, configuration }) {
+    console.log('Wiring up important stuff.');
+
+    window.importantStuff = () => {
+      console.log(configuration);
+    };
+
+    console.log('Important stuff has been wired.');
+    window.importantStuff();
+  },
+};
+```