Fix current user missing in Google Analytics

[MrOrz]

The issue is found in 20220706 meeting

Currently on production, if the user is already logged in, starts their session on the landing page, and then goes to other pages, their user ID will not be sent in Google Analytics actions.

This is because

• We push current user to Google Tag Manager in useCurrentUser's onCompleted callback
  
• Before this PR, landing page uses its own way to load user, and thus does not use useCurrentUser
• Landing page loads all fields that is required by useCurrentUser, so that when user enters other page from landing page, useCurrentUser hook will not invoke new GraphQL queries, thus not calling onCompleted callback at all.

This PR fixes the issue by using useCurrentUser in landing page as well.

Screenshot

Before

CURRENT_USER is not pushed to dataLayer even after the user logs in on landing page

After

Can see that CURRENT_USER is pushed to dataLayer as expected.

[coveralls]

Coverage remained the same at 75.605% when pulling 9cda373 on fix-current-user into eb4d12d on profile-filter-count.