Merge bitcoindevkit/bdk#884: Update esplora client dependency to version 0.4

bb2b2d6dd8949a84675554c05b9880199c460fcf Update esplora-client dependency to version 0.4 (Steve Myers)

Pull request description:

  ### Description

  Update the `esplora-client` to the new `0.4` release.

  ### Notes to the reviewers

  The `esplora-client` was updated in bitcoindevkit/rust-esplora-client#39 to not include default `rust-bitcoin` dependencies.

  ### Changelog notice

  - Update the `esplora-client` optional dependency to version `0.4`.

  ### 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:
  vladimirfomene:
    ACK bb2b2d6dd8949a84675554c05b9880199c460fcf
  rajarshimaitra:
    tACK bb2b2d6dd8949a84675554c05b9880199c460fcf

Tree-SHA512: 0f277106166ab4a8144a641ac9507f1a32d735f99c0b73a026ff6e0b82589110a71fe81f880caa01dab247572f3146b771cc28bdab5b22bcd87ff628e15b2e1a