Slyghtning

This PR so far has only taken https://github.com/lightningnetwork/lnd/pull/4029 and rebased it with the latest master. Next steps are to make the build pipeline checks succeed and then address the comments...

Thanks @guggero, yes good point. I will attribute the commits to Bjarne.

I've went through the parent PR top to bottom and now have a better grasp of what the difficulties were up to this stage and how some of them were...

@saubyk I don't see psbt scenarios covered in the parent PR. I am currently incorporating requested changes to the `itest` and am at this stage to add a test for...

@guggero I think I've addressed all the changes you and others had requested in the previous PR https://github.com/lightningnetwork/lnd/pull/4029 and linked them to this PR starting from your comment here:https://github.com/lightningnetwork/lnd/pull/4029#pullrequestreview-866128472. Furthermore...

> > Sure, anything that makes our lives easier in the future is nice. Though I'm not sure it's an easy thing to do. Since we don't yet know what...

Thanks for the review @guggero - would you also be able to comment on my questions above about a new test case and the `psbt`/`fundmax` behavior? --> https://github.com/lightningnetwork/lnd/pull/6903#issuecomment-1254996287

@guggero I think I addressed all the issues you flagged in your last review and tried to stick to the 80 char line limit in a bunch of other places....

Hi @joostjager, yes I agree - I will add context about the motivation and details of this PR in the description in a bit.

Re your points @guggero > @hieblmi sorry for the late answer. Here's my input to your three questions: > > 1. Ah yes, good catch. I agree that we should...