Merge bitcoindevkit/bdk#681: Add `electrsd/bitcoind_22_0` to `example\rpcwallet`...

Merge bitcoindevkit/bdk#681: Add `electrsd/bitcoind_22_0` to `example\rpcwallet` target

a63c51f35dc392bfcd390cbda0eb40205b78ac8e Add `electrsd/bitcoind_22_0` to `example\rpcwallet` target (w0xlt)

Pull request description:

  On master branch, `example\rpcwallet` fails.

  ```
  $ cargo run --features="keys-bip39 key-value-db rpc" --example rpcwallet
     Compiling bitcoin_hashes v0.9.7
     Compiling bip39 v1.0.1
     Compiling bdk v0.20.1-dev (/home/node01/Dev/wbdk)
      Finished dev [unoptimized + debuginfo] target(s) in 19.64s
       Running `target/debug/examples/rpcwallet`
  >> Setting up bitcoind
  thread 'main' panicked at 'We should always have downloaded path: Called a method requiring a feature to be set, but it's not', examples/rpcwallet.rs:56:51
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
  ```

  This PR adds `electrsd/bitcoind_22_0` to `required-features`, making clear that this lib is needed to run this example..

  ```
  $ cargo run --features="keys-bip39 key-value-db rpc electrsd/bitcoind_22_0" --example rpcwallet
      Blocking waiting for file lock on package cache
     Compiling electrsd v0.19.1
     Compiling bdk v0.20.1-dev (/home/node01/Dev/wbdk)
      Finished dev [unoptimized + debuginfo] target(s) in 10.27s
       Running `target/debug/examples/rpcwallet`
  >> Setting up bitcoind
  >> bitcoind setup complete
  Available coins in Core wallet : 50.00000000 BTC

  >> Setting up BDK wallet
  >> BDK wallet setup complete.
  Available initial coins in BDK wallet : 0 sats

  >> Sending coins: Core --> BDK, 10 BTC
  >> Received coins in BDK wallet
  Available balance in BDK wallet: 1000000000 sats

  >> Sending coins: BDK --> Core, 5 BTC
  >> Coins sent to Core wallet
  Remaining BDK wallet balance: 499999859 sats

  Congrats!! you made your first test transaction with bdk and bitcoin core.
  ```

ACKs for top commit:
  afilini:
    reACK a63c51f35dc392bfcd390cbda0eb40205b78ac8e

Tree-SHA512: ef13d5e001121c8b1ff6436f9e95b656737bee6692e9b18c4012846a2d2e9e9ad7e6b5cd87cebf4a873335e92a524694e684567a1268f5f0705156659fd9a916