Move `bdk_wallet` crate to new `bdk_wallet` repo

[notmandatory]

This will require:

• clone bdk repo and rename it to bdk_wallet
• remove crates and other files not related to bdk_wallet
• update ci workflows
• make PR to remove bdk_wallet from bdk repo
• transfer "BDK Wallet" issues to bdk_wallet repo
• comment on "BDK Wallet" PRs requesting they push / recreate in bdk_wallet repo
• update crates.io bdk_wallet repo location

[notmandatory]

See dry run here: https://github.com/notmandatory/bdk_wallet/

The plan is to do this change right after the 1.2 tag is made.

[notmandatory]

One caveat, I can move issues but not PRs, so current wallet PR owners will need to manually re-create their PRs in the new bdk_wallet repo. I'll put some instructions together to make this easier. There are currently 40 PRs this applies to: https://github.com/bitcoindevkit/bdk/pulls?q=is%3Aopen%20is%3Apr%20project%3Abitcoindevkit%2F14

[notmandatory]

Steps to move bdk_wallet related PRs to the new bdk_wallet repo:

1. From your Github account, fork https://github.com/bitcoindevkit/bdk_wallet
2. From your local system bdk repo folder, push your PR changes to your bdk_wallet fork on Github:

   git checkout <PR branch path>
   git push git@github.com:<username>/bdk_wallet.git
   

3. Clone to your forked bdk_wallet repo to your local system and switch to your PR branch:

   git clone git@github.com:<username>/bdk_wallet.git
   cd bdk_wallet
   git fetch origin <PR branch path>
   git checkout -b <PR branch path> FETCH_HEAD
   git rebase master
   

4. Resolve rebase conflicts (if any)
5. Force push your PR branch: git push origin -f
6. Create new PR in bitcoindevkit/bdk_wallet repo from your fork branch
7. Copy/paste title and description from your original bdk PR and add a link back to it in your new PR.
8. Close original PR with comment that includes link to new PR.

[notmandatory]

bdk_wallet PR to remove non-wallet files and other cleanup is #2.

[luisschwab]

We also need to update this repo's README pointing to the new bdk_wallet or remove the reference entirely.

[luisschwab]

And also rename example-crates to examples to keep it consistent.

[notmandatory]

PR to remove bdk_wallet from the bdk repo is bitcoindevkit/bdk#1928 .