Also added splice_out tests that use the new PSBT command.
ChangeLog-Added: New `addpsbtoutput` command for creating a PSBT that can receive funds to the on-chain wallet.
Added a test for splicing out that exposed some behavior and code glitches that are addressed in this commit.
Added test for splice gossip.
Also added documentation for how to do a splice out.
ChangeLog-Fixed: Added docs, testing, and some fixes related to splicing out, insufficent balance handling, and restarting during a splice.
Update the lightningd <-> channeld interface with lots of new commands to needed to facilitate spicing.
Implement the channeld splicing protocol leveraging the interactivetx protocol.
Implement lightningd’s channel_control to support channeld in its splicing efforts.
Changelog-Added: Added the features to enable splicing & resizing of active channels.