Add glu to help menu

What does this MR do and why?

GitLab University is not currently discoverable from GitLab (CE and EE), which means we're missing a key opportunity to drive awareness of our learning platform and connect users with relevant training resources and certification information.

This MR adds a link to GitLab University on the Help menu on GitLab (CE and EE).

References

:link: Related issue

Screenshots or screen recordings

Before	After

How to set up and validate locally

MR acceptance checklist

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