Merge bitcoindevkit/bdk#519: Add wallet creation example using RPC

8a98e69e788dd79d030798465fbc0dec044d86f1 Add rpc wallet creation example (rajarshimaitra)

Pull request description:

  ### Description

  As mentioned in https://github.com/bitcoindevkit/bitcoindevkit.org/issues/83#issuecomment-1005190174 it would be helpful
  to have wallet creation example code in the `example` directory.

  This is an attempt to create the most simplistic bdk wallet with a RPC backend and demonstrate receiving, creating, signing
  and broadcasting transaction.

  The code is a refinement of the RPC tutorial https://bitcoindevkit.org/blog/bitcoin-core-rpc-demo/ with more elaborate doc comments.

  ### Notes to the reviewers

  To automate the background RPC process `electrsd` is used which is already a `dev-dependency` of bdk.

  ### Checklists

  #### All Submissions:

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

ACKs for top commit:
  notmandatory:
    tACK 8a98e69e788dd79d030798465fbc0dec044d86f1

Tree-SHA512: f00c1ce57ef91c3d3ab2ce08af3571c41bbe98f18f705c61ba4217c2f8061196e5eaf6122742293cd6fa16939bbbfacd0f8506cd4151b55f19a05325fd94a74a