Merge bitcoindevkit/bdk#1287: doc(store): update doc for `Store::aggregate_changesets`

Merge bitcoindevkit/bdk#1287: doc(store): update doc for `Store::aggregate_changesets`

3829fc18c7f2d16d2c72852bde4b4b70bff8e370 doc(store): update doc for `Store::aggregate_changesets` (vmammal)

Pull request description:

  ### 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:
  evanlinjin:
    ACK 3829fc18c7f2d16d2c72852bde4b4b70bff8e370

Tree-SHA512: 55e3dea6db4e023edcd6f12e3c2e8f63c79654b178e01e2fb8b66f3a66399aabedb1d159cd015b78bc2166be6e640e0ed684e3571f2c4f2f6a53fa68d2ef9849