Create projects for all examples in our docs

[matevz]

After oasisprotocol/docs#1585 is merged, find all :::example occurrences and create playground cards for them. Add meaningful screenshot, if possible. Don't forget to mark them as "Maintained by Oasis". Tag them accordingly (at least "ROFL").

This will enable us to create a URL that filters these examples and makes a QR code in the Oasis cheatsheet.