Merge bitcoindevkit/bdk#589: export: Rename `WalletExport` to `FullyNodedExport`

9ed36875f1112d884f6c3c2beab89faf8aa5d2e0 export: Rename `WalletExport` to `FullyNodedExport` (Alekos Filini)

Pull request description:

  ### Description

  The `WalletExport` type can still be used as an alias to `FullyNodedExport` but it has been marked as deprecated and will be removed in the next release.

  ### 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

  #### New Features:

  * [ ] 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:
  bucko13:
    Concept ACK 9ed3687
  notmandatory:
    ACK 9ed36875f1112d884f6c3c2beab89faf8aa5d2e0

Tree-SHA512: fe07307092d3040b30ae96901d5fc4afecee635412bca4a0d2e78d90f07990e7bbcd6b87ed923bf5804385356f419cacadbfefbaf97ebc9a622e34548438ee00