Upgrade example_cli

[ValuedMammal]

fixes #1469

• Adds two commands init and generate. Loading database doesn't require descriptors
• Replaces send command with psbt (new, sign, and extract). Supports tap key spend
• Graduate from the nursery

Notes to the reviewers

Changelog notice

Checklists

All Submissions:

• [ ] I've signed all my commits
• [ ] I followed the contribution guidelines
• [ ] I ran cargo fmt and cargo clippy before committing

[storopoli]

We could merge this with #1442 and then commit it as a single PR?

If favorable I could rebase #1442 and then you can commit on top of that? Or I can do the opposite as well...

[ValuedMammal]

1442 can be merged anytime and from what I can tell doesn't conflict with this one

[rustaceanrob]

Nice. This cleans things up quite a bit.

[ValuedMammal]

• Rebased onto 17a9850cba06db837b82cef1dbaf2ef1e342f7ec
• For now I'm using bdk_wallet::ChangeSet for the example-cli
• Added back support for single descriptor use
• CI failed to build msrv

[ValuedMammal]

Thanks @evanlinjin @LLFourn

We're currently limited to creating PSBTs for wpkh and tr descriptors because I got stuck on trying to add assets/keys for wsh (can still sync and derive addresses though).

[evanlinjin]

@ValuedMammal I think that's fine for now, can add them later