Add key-value-db and sqlite-db features, separate wallet directories

[notmandatory]

Description

• Add distinct key-value-db and sqlite-db features, keep default as key-value-db

• Put cached wallet data in separate directories: ~/.bdk-bitcoin/<wallet_name>

• Put compact filter data in <wallet_name>/compact_filters

• Depending on the db used put cached wallet data in: <wallet_name>/wallet.sled/ or <wallet_name>/wallet.sqlite

Notes to the reviewers

This change will help test BDK with different databases, in particular for manually testing DB migrations such as in https://github.com/bitcoindevkit/bdk/pull/502.

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:

• [ ] I've added tests for the new feature
• [x] I've added docs for the new feature
• [x] I've updated CHANGELOG.md

[notmandatory]

@rajarshimaitra can you take a look at this one?

EDIT: Never mind for now, I'm moving this back to draft so I can make the DB features additive per #75.

[notmandatory]

@rajarshimaitra I changed my mind again on the additive features thing. I still think it'd be good to try but will be a biggish change (if it's even possible) for bdk-cli and probably not worth the effort right now.

This PR is now rebased and should be ready to go.