Fetch DIDs through ceramic as well as address DB

Because new versions of the 3box-js client will use ceramic to link addresses, to allow outdated clients to access these links, the address server should be able to fetch and serve these links through ceramic as well.

This should also include the rootstore address derivation from DID so that the address DB can be deprecated in the future.

The issue involves updating the address server to fetch DIDs through Ceramic, not just the address DB. Start by examining the server's current data fetching logic and the 3box-js client integration. Understand how rootstore address derivation from DID works to allow deprecation of the address DB. Check for existing Ceramic client setup or need to add it, and ensure backward compatibility for outdated clients.

索引モデルが issue の本文から書いたものです。