Normal Swaps: Batched Key Path Spends

[kilrau]

https://github.com/BoltzExchange/boltz-backend/pull/478 implemented batched normal swap claims via script path spends. Since batching is preferred when volume is high, we want to bring Taproot's privacy features and efficiency to batched claims too.

For always-on clients only. This requries all client of the batch to be online and cooperating in the moment of the claim. They probably should get a discounted rate and set a flag for participating in batching.