Docs: Update to reflect that Admin Area is available on left sidebar

Previously, the Admin Area was available from Search or go to. However, now it is also available at the bottom of the left sidebar.

This issue is to update all the docs and the style guide to change the guidance from:

1. On the left sidebar, select Search or go to.
2. Select Admin Area.

To:

1. On the left sidebar, at the bottom, select Admin Area.

Tasks

Need to do all the repos:

• gitlab
• runner (no instances of "Admin Area" found)
• charts
• omnibus
• operator (no instances of "Admin Area" found)

Screenshots

Before

Previously it was available by selecting Search or go to:

After

Now it is at the bottom of the left sidebar: