Track the cp `node_id` which originated an HTLC in the `HTLCSource`

Track the cp `node_id` which originated an HTLC in the `HTLCSource`

Because we track pending `ChannelMonitorUpdate`s per-peer, we
really need to know what peer an HTLC came from when we go to claim
it on-chain, allowing us to look up any blocked actions in the
`PeerState`. While we could do this by moving the blocked actions
to some global "closed-channel update queue", its simpler to do it
this way.

While this trades off `ChannelMonitorUpdate` size somewhat (the
`HTLCSource` is included in many of them), which we should be
sensitive to, it will also allow us to (eventually) remove the
SCID -> peer + channel_id lookups we do when claiming or failing
today, which are somewhat annoying to deal with.