Add Decentralized Identity #102

https://developers.ceramic.network/docs/advanced/standards/accounts/3id-did/

Acceptance criteria:
Allow for a cryptographically enabled identity to be used in a signing flow where currently User log-in is maintained by the centralized user table.

To see this flow in action check out https://app.orbis.club

To summarize, the identity flow can proceed by:
0. connect wallet (public / private key pair in disguise)

1. sign a string with your private key to show you are who you claim you are
2. receive a session that will allow tying your Collections to be tied to a decentralized identifier and eventually composable with other services (not in scope for this issue, which is simply to add the signing flow)

The source of DID does not need to be a wallet -- for instance, proofs ("stamps") for Gitcoin Passport can come from LinkedIn, Facebook, Twitter, and any number of existing OAuth-using services.