Add Case studies on the homepage

[Zelig880]

Add a banner for the case studies on the homepage.

NOTE: it is the first design in figma, the one with opacity!

AC:

• [x] Add banner on the homepage
• [x] The case studies you show can be random (as we do with the rest )

Figma: https://www.figma.com/file/9eqpfWUrL3gAQ6Royvl75u/Blockchain-Education?node-id=10939%3A79803