Summary

Hermes needs to be able to process documents received via IPFS PubSub channel.

Description

Hermes node should get a doc from PubSub, process it and trigger the "on-new-doc" event in the client

What needs to happen upon receiving the PubSub notification:

1. The notification is processed in subscription_stream_task (the message contains data: Vec<u8>)
2. data is interpreted as document
3. the document is pinned
4. trigger the client-side on-new-doc event
5. we do not publish the doc further