Merge bitcoindevkit/bdk-cli#115: Use async with esplora-reqwest

8d876ef376097e6361d9f8495afb82a3ef03b87b Use async with esplora-reqwest (Daniela Brozzoni)
a9dffc3a6ca1834f11b00cda27d2466423096e41 Remove wrong 'cfg()' (Daniela Brozzoni)

Pull request description:

  ### Description

  We previously had the esplora-reqwest feature, but it would use
  sync reqwest, as the "async-interface" feature in BDK wasn't set.
  This commit sets this feature so that using `esplora-reqwest` always
  uses async mode.

  ### Notes to the reviewers

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

ACKs for top commit:
  afilini:
    reACK 8d876ef376097e6361d9f8495afb82a3ef03b87b

Tree-SHA512: 3e6c8ebc0c9ac772f28a6282b7478b436d519fdd081e98f282c00d520cc2ed400636407be2e4ba9f9203bd7141cc35bdc85430f9689c300f01945b76d411cf68