Merge bitcoindevkit/bdk#930: Add default `std` feature, prep for 0.28.0 release

Merge bitcoindevkit/bdk#930: Add default `std` feature, prep for 0.28.0 release

cbcbdd120d48742ed70fcb47c159266ae6c5b1ae Update CHANGELOG for 0.28.0 release (Steve Myers)
f5071857294f3a0002aa3e2774f86a588ac4af3e Change workflows to run for release branches (Steve Myers)
573bf52578d0f3e93b9dae7f17faffc3aad3839b Add default feature std (Steve Myers)

Pull request description:

  ### Description

  Add new `std` feature which enables `bitcoin/std` and `miniscript/std`, and enable `std` feature in `default` feature set.

  ### Notes to the reviewers

  When using `bdk` in a wasm environment then `default` features should be disabled and `bitcoin/no-std` and `miniscript/no-std` must be enabled.  This is a breaking change for anyone using `bdk` with `--no-default-features`.

  I also updated the workflows to also run for `release/*` branches in addition to `master`.

  ### Changelog notice

  Changed

  - Added new `std` feature as part of `default` features, `std` must be enabled unless building for wasm.

  ### 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

ACKs for top commit:
  rajarshimaitra:
    ACK cbcbdd120d48742ed70fcb47c159266ae6c5b1ae

Tree-SHA512: fc0e1495d2f4e65c015d771366ac8d9589736b4464cf496de5093cdef145abfed037c0701c3c210f70a7bde5128b681492202cecfca7cd94771d498e8fb8e565