Resolve "Add missing snowplow tracking to primary navigation"

What does this MR do and why?

Fires structured snowplow events for actions which currently lack them. Specifically, this adds events to the main menu toggle button (the hamburger icon), and the focus state of the global search input.

Screenshots or screen recordings

after global search focus

after global search blur and menu toggle

How to set up and validate locally

1. Set up Snowplow tracking in your local GDK instance
2. Install the Snowplow debugger Chrome extension
3. Navigate to your local GDK and sign in
4. Visit any page where the top navigation menu is visible
5. Open the snowplow debugger panel
6. Click on the navigation menu toggle and notice the click_nav event is firing with label hamburger_menu
7. Click on the global search input and notice the focus_input event is fired with label global_search
8. Click anywhere else to blur the field and notice the blur_input event is fired with label global_search

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #376712 (closed)

spec/frontend/nav/components/top_nav_app_spec.js

 import { GlNavItemDropdown } from '@gitlab/ui';
 import { mount, shallowMount } from '@vue/test-utils';
-import Tracking from '~/tracking';
+import { mockTracking } from 'helpers/tracking_helper';
 import TopNavApp from '~/nav/components/top_nav_app.vue';
 import TopNavDropdownMenu from '~/nav/components/top_nav_dropdown_menu.vue';
 import { TEST_NAV_DATA } from '../mock_data';
@@ -58,12 +58,15 @@ describe('~/nav/components/top_nav_app.vue', () => {
 
   describe('tracking', () => {
     it('emits a tracking event when the toggle is clicked', () => {
-      const eventSpy = jest.spyOn(Tracking, 'event');
+      const trackingSpy = mockTracking(undefined, wrapper.element, jest.spyOn);
       createComponent();
 
       findNavItemDropdowToggle().trigger('click');
 
-      expect(eventSpy).toHaveBeenCalledTimes(1);
+      expect(trackingSpy).toHaveBeenCalledWith(undefined, 'click_nav', {
+        label: 'hamburger_menu',
+        property: 'top_navigation',
+      });
     });
   });
 });