There should be a way to insert blocks during runtime

Currently, there isn't mechanism to notify the behaviour that new blocks have been inserted into the blockstore manually (rather than coming from bitswap network). While new incoming requests for inserted CID will be processed properly, if there's a peer that requested that CID before it's inserted, they won't be sent this block on insertion.

idea: have blockstore be accessable through the behaviour, so that it can be notified of new CIDs and react to them.

Start by tracing how the behaviour accesses the blockstore and handles pending requests for CIDs received through the bitswap network. Define an insertion notification path for manually added blocks, and consider the issue done when peers waiting for an inserted CID receive it while existing incoming-request handling continues to work.

Written by the indexing model from the issue text.