feat: redesign-usecaes-overview

[wesleyboar]

Overview

Redesign Use Cases overview, so user can navigate from the page (because they are not familiar with sidebar yet).

Status

• [x] layout & style
• [x] card descriptions
• [x] do not expand "Overview" in side nav
• [x] card images

Changes

• added global css to remove footer on new layout
• added content and layout to usecases/overview

Testing

1. Open https://pprd.docs.tacc.utexas.edu/usecases/overview/. _{(or, locally, http://0.0.0.0:8000/user-guide/usecases/overview/)}
2. Evaluate.

UI

top	end

[wesleyboar]

[Internally] I interpreted approval from @silviamazzoni [and] received only positive feedback from @cs-jansen, so I merge.