shut down worker service gracefully whenever any parentchain dispatches System.CodeUpdated event

[brenzi]

As a simple solution to the change in metadata and runtime spec_version and transaction_version, we could just shut down the service gracefully and have it restart automatically.

caveats:

• TOP pool will be lost. Not dramatic, as no user got a confirmation. submission will just time out or abort
• When the System.CodeUpdated event is dispatched, it is already too late to send extrinsics with the wrong AdditionalParams. If we want to prevent this transient risk, we need to shut down already at System.UpgradeAuthorized and await the upgrade
  • one solution could be to reject TOPs which cause extrinsiscs on parentchains to be rejected after UpgradeAuthorized. this would minimize downtime while maintaining consistency

[clangenb]

What is a bit of a nuisance though, is that the worker registers every time upon restart. maybe the worker can check if it has been registered lately, and skip registering in order to cut down the restart time?