Send updates to the new shard during resharding

[ffuugoo]

Tracked in #4213.

This PR enables sending update to the created shard and adds basic error handling for failed updates.

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[ffuugoo]

This still feels a bit "hacky", IMO, but I don't want to spend more time on this RN. I propose we merge it, and then improve on it once we started working on the resharding driver.

[timvisee]

How about doing this in sync_local_state, like we do with shard transfers?

[ffuugoo]

Can you elaborate? abort_resharding does not send any consensus messages. It actually aborts resharding locally. We also abort shard transfers on Dead state in the same way (just a few lines below selected snippet).

[timvisee]

👍

I missed that bit.

Where should we produce the abort resharding concencus call though? Should the driver itself be responsible for this?

[ffuugoo]

Either user aborts explicitly, or the driver (e.g., if one of the transfers failed). When update fails we just propose peer Dead and abort when applying this state change.