Merge bitcoindevkit/bdk#846: Update CHANGELOG and release process

4ada11f3581a172ec2d5980378267f578e998740 Update CHANGELOG and release process (Steve Myers)

Pull request description:

  ### Description

  Per discussion on discord with @danielabrozzoni this PR updates our release process to go back to updating our CHANGELOG.md file for each release.

  ### Notes to the reviewers

  This adds one more step the person making releases has to do but it isn't much.

  ### 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)

ACKs for top commit:
  danielabrozzoni:
    ACK 4ada11f3581a172ec2d5980378267f578e998740

Tree-SHA512: 80c116c90b4a5c5d4091678dd7714c9eee881c0f181dd220e878011001ad458db2bb81dea7dc13f2d768b9169c3644191d7969c533b784a5e26f5aa6c9e66fc2