feat!: Disaster recovery via gateway

[cdata]

This change proposes a disaster recovery mechanism where an embedding Noosphere client may take advantage of an existing gateway to restore a user's local sphere data.

In order to recover data from a gateway, the following information is needed:

• URL of the gateway
• The DID of the user's sphere
• The name of an authorized device key
• The user's recovery mnemonic

The Noosphere library then generates an ephemeral, one-time-use authorized credential and uses it to perform the fetch half of a gateway sync. After the sync completes, it ensures that the local storage layer is properly configured to use the original device key.

[jsantell]

looking forward to this one

[cdata]

Continuing the trend of forcing lint checks for missing documentation on a crate-by-crate basis, I added #[warn(missing_docs)] to the noosphere crate and filled in the gaps where docs were missing.