anchor RSVPs on a smart contract (decentralized case)

[elmariachi111]

• Requires the user to be authenticated with an SSI/DID (3box)
• to signup, send a transaction with your public address to a contract's "signup" function
• the organizer now knows, which "public addresses" / 3box identities will join.
• in a good case he also knows who's the real person behind that address (3box identity)
• in the best case that identity contains a mail address where the organizer can send notification emails to.
• some sample code (defunct) here: https://github.com/cod1ng-earth/ce-website/tree/contracts/api
• decide wether each event needs its own smart contract instance. We can simply anchor its GraphCMS id in a mapping on the base contract and rsvp users by adding their address to a list