Resolve "Track navbar clicks on GitLab.com"

What does this MR do?

In 11.4 we've introduced a generic event listener for tracking custom click events

Based on this, the MR adds tracking to the following navbar events:

• Projects dropdown open
• Projects dropdown close
• Groups dropdown open
• Groups dropdown close
• "+" dropdown open
• "+" dropdown close
• Profile dropdown open
• Profile dropdown close
• Projects search bar
• Groups search bar
• Global search bar

CE port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23975

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/7427

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?

Closes #7427 (closed)