[WIP] Implement create_psbt for Wallet

[ValuedMammal]

Description

Use the new bdk_tx transaction building library to create PSBTs in BDK Wallet. Primary benefits include the use of bdk_coin_select as well as miniscript::plan module under the hood.

In this PR:

• Add method create_psbt for Wallet.
• Add module wallet::psbt_params
• Add example wallet/examples/psbt.rs

Notes to the reviewers

Still in draft but feel free to comment and make suggestions.

Changelog notice

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines

New Features:

• 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
• I'm linking the issue being fixed by this PR

[coveralls]

Pull Request Test Coverage Report for Build 17239231069

Details

• 0 of 185 (0.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-2.0%) to 82.958%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
wallet/src/wallet/psbt_params.rs	0	54	0.0%
wallet/src/wallet/mod.rs	0	131	0.0%

Totals
Change from base Build 17132535147:	-2.0%
Covered Lines:	6669
Relevant Lines:	8039

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💛 - Coveralls

[thunderbiscuit]

I like the create_psbt name for the function. The Params struct I need to do a quick search but off the top of my head it feels like we have a few of those scattered across the crates named exactly that, so it gets confusing. In my exploration PR I used TransactionParams, but that's a bit long and verbose.

What do you envision the API for replace-by-fee transactions look like in this new bdk-tx world? I'm picturing something like Wallet::create_replacement_psbt which takes a WalletTx and another Params struct.