Detect 'halted' state of pallets in relay

[svyatonik]

Right now if bridge pallets (GRANDPA/messages) are halted, relay will keep submitting transactions, wait for timeout and then resubmit the same transactions again. This is fine for testnets, but wasting real-value chain resources isn't a good idea. So relay shall detect pallets state and pause if pallet is halted.

The best way to implement that is to add this logic to the ensure_synced() method of the client.