[hf] bump `availableSockets` config (to actually increase shards)
- in MR !516 (merged) (in which we migrated to a larger server) we also sought to leverage the increased RAM to increase the number of signald shards
- however, though more signald containers are running, we are not
currently talking to them b/c we neglected to increase
app.config.socket.availableSockets
from 5 to 8 - this MR fixes that