ChainHead APIs: add option to timeout subscriptions if no events received in N seconds #2050
Description
See paritytech/polkadot-staking-miner#1119 (comment)
On occasion, these subscriptions seem to stop receiving events. It's not clear why offhand, but would be good to be able to catch and handle such failures. The obvious way to do this is having a timeout such that if no more events are received for a certain amount of time, assume something went wrong / recreate the subscription.
For now, we could add a configurable timeout in the ChainHead backend which errors out if it stops receiving events. This owuld also cover runtime updates, and anything else using the same stream.
I perhaps would add similar the the legacy APIs, though offhand can't recall if we could do something nice for runtime updates or not.