Merge bitcoindevkit/bdk-cli#68: Add cookie authentication option for rpc

1ab2b0ffc780defa913ec9ce2dc021b355c2aeb3 Fix docs test for WalletOpts (Steve Myers)
a9f14a9a4d05d833deee66113319cd6bc8b3f641 Update CHANGELOG (rajarshimaitra)
180fe4748c85dde7668785abf8593c1a34c55238 Add cookie authentication option for rpc (rajarshimaitra)

Pull request description:

  ### Description

  Fixes https://github.com/bitcoindevkit/bdk-cli/issues/67

  This PR adds an optional `cookie` arg to pass on cookie file if user needs to use that instead of basic user:password based authentication.

  bitcoin core will only generate a `.cookie` file if rpc username passwords are not set in `bitcoin.conf`. Thus cookie file doesn't have a default. User should only provide it if they know a cookie file exists, or else "File not found" error is returned.

  ### 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:

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

ACKs for top commit:
  notmandatory:
    ACK 1ab2b0ffc780defa913ec9ce2dc021b355c2aeb3

Tree-SHA512: 164f8c65582028efa36035f5a442b7d1678a19ef74196286f29e10dad79cb3495fe1b3ac46207eca55115d6a7744e94ddf333238b1933bc7586df049062b670b