We need to use it for the 'df_accepter' plugin, so we get the feerate
correct.
Changelog-Added: pyln-client: `fundpsbt`/`utxopsbt` now support `min_witness_weight` param
We let the plugin decide what feerate to accept/whether or not to add
funds to the open. To aid this decision, we also send the plugin what we
(c-lightning) currently have as our max and min acceptable feerates.
We also now use these as our default for max/min acceptable feerate
range when sending an openchannel offer to a peer.
In the future, it might be a good idea to make these more easily
changeable, either via a config setting (?) or a command param.
