the update_fee logic for lightning channels was not adapted to anchor
channels causing us to send update_fee with a eta target of 2 blocks.
This causes force closes when there are mempool spikes as the fees we
try to update to are a lot higher than e.g. eclair uses. Eclair will
force close if our fee is 10x > than their fee.
- Wallet.make_unsigned_transaction takes a FeePolicy parameter
- fee sliders act on a FeePolicy instead of config
- different fee policies may be used for different purposes
- do not detect dust outputs in lnsweep, delegate that to lnwatcher
