fix(export): add tr descriptor

[rustaceanrob]

Description

Resolves #860 by adding export of taproot descriptors

Notes to the reviewers

Allows export as Core accepts taproot.

Changelog notice

• Export taproot descriptors

Checklists

All Submissions:

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

New Features:

• [x] I've added tests for the new feature
• [ ] I've added docs for the new feature

Bugfixes:

• [ ] This pull request breaks the existing API
• [ ] I've added tests to reproduce the issue which are now passing
• [x] I'm linking the issue being fixed by this PR

[ValuedMammal]

Concept ACK

[oleonardolima]

@notmandatory I think this one is missing the 1.0.0-alpha label, as it was on the #860, could you add to it, please ?