Expose "transaction transcript" in ChannelMonitor

[TheBlueMatt]

We really should have a way to figure out full channel-closing cost which would need to happen via ChannelMonitor. It shouldn't be too wildly complicated - once we have 6 confs on the funding-spending transaction we just need to map each output to the msat value of the output and how much we actually end up claiming, probably via a "transaction transcript" that tells users what transactions were used to claim all our balances.

cc https://github.com/orgs/lightningdevkit/discussions/2405