Update admin docs with new admin area access info

What does this MR do?

GitLab 14.0 includes an interface change that moves the UI element to access the Admin Area to a new location; from the top menu bar to within the Menu option on the top menu bar.

This updates the administration documentation pages that describe accessing the Admin Area to reflect the new interface change.

Related issues

For #333270 (closed)

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Edited by Achilleas Pipinellis (OOO | back on july 25th)