[yjs] Replace old seed grant mechanism with new generic grants #3436

#3433 replaces the seed grant mechanism of the yjs server via _oc_seed_* with a more generic way via _oc_grant_*:. The client however still uses the old way, until most of the yjs servers out there have been updated to the new versions. Once adoption for the new yjs server has increased, we need to migrate the client to the new mechanism and remove the old code paths.