Sync beefy commitment on demand

[yrong]

A one-shot relayer at this moment and how we would integrate the one-shot relayer in future as follows from @vgeddes:

1. User on Polkadot signals that they want to speed up their message by depositing a fee in a special account on AssetHub/BridgeHub
2. An offchain service witnesses that deposit, and invokes the one-shot relayer

[vgeddes]

Still need to adjust for the change in parameters.go: https://github.com/Snowfork/snowbridge/pull/1216/files#diff-e3b26e6a7128d75b5212e1dcbf97eb9f68934a321bd0d45990894a40f2b7cc24L168

Only submissions for mandatory commitments need to include an MMR leaf and proof. The one-shot relay doesn't need to include those.

[yrong]

Only submissions for mandatory commitments need to include an MMR leaf and proof. The one-shot relay doesn't need to include those.

I'd prefer to include the MMR leaf and proof for the oneshot case, vaguely recalled it won't cost much to add these to calldata without validation. The benefit is that it's possible to use the oneshot command for even sync the mandatory commitments.