Merge bitcoindevkit/bdk-cli#200: feat: add non-persisted Async Payjoin support

c6bce58871e23c26d116e5c7b767ff4209a7b3c4 docs: add Payjoin capability to the README (Mehmet Efe Umit)
4cab2fa8f4d4b7fe95453bf3391019cf2dd4d7aa feat: add payjoin receive support (Mehmet Efe Umit)
0112c924adf186b8b62d77d8dc0b2837426ea4af feat: add payjoin send support (Mehmet Efe Umit)
f62287aff383555a301fd62be40064e1c54ec119 refactor: move broadcast to a helper function (Mehmet Efe Umit)
a28076af9b1016d5456de6c2b81d502beb05737d refactor: move sync to a helper function (Mehmet Efe Umit)

Pull request description:

  ### Description

  This change implements the online commands for both sending and receiving a Payjoin. Note that this PR does not implement Payjoin persistence.

  ### Notes to the reviewers

  Tested on my local regtest with rpc  using the OHTTP relays and directories in the [payjoin-cli README](https://github.com/payjoin/rust-payjoin/tree/master/payjoin-cli). Feel free to do the same, and let me know if there are comments, documentation, etc. which should be changed with this. I was not able to find any...

  Here are the sample command you can use to test on regtest:

  **Send**
  ```
  cargo run --features=rpc -- -n regtest wallet -a USERNAME:PASSWORD -w WALLET_NAME -e "DESCRIPTOR" send_payjoin --ohttp_relay "RELAY1" --ohttp_relay "RELAY2" --fee_rate 1 --uri "URI"
  ```
  **Receive**
  ```
  cargo run --features=rpc -- -n regtest wallet -a USERNAME:PASSWORD -w WALLET_NAME -e "DESCRIPTOR" receive_payjoin --max_fee_rate 1000 --directory "https://payjo.in"  --ohttp_relay "RELAY1" --ohttp_relay "RELAY2" --amount AMOUNT
  ```
  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [X] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk-cli/blob/master/CONTRIBUTING.md)
  * [X] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [] I've added tests for the new feature  <--- There is no testing suite for this.
  * [X] I've added docs for the new feature
  * [N/A] I've updated `CHANGELOG.md`

  #### 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

ACKs for top commit:
  tvpeter:
    tACK c6bce58871e23c26d116e5c7b767ff4209a7b3c4
  spacebear21:
    utACK c6bce58871e23c26d116e5c7b767ff4209a7b3c4

Tree-SHA512: 1da8295d0eedf6fd31095085e6ef0d90ab46d5eed6c2f21a7539a6c3ff6d1127d0cdbb664d519bcb4a783ea2707452bf8cd3cb961a67ba3e61d989701e205dca