Support parsing release notes from changelog files

[Goooler]

As Keep a Changelog described, a good changelog should look like:

## [Unreleased]


## [1.1.1]
### Added
- 1
- 2
### Fixed
- 3
- 4
### Changed
- 5
- 6


## [1.1.0]
...

We can do something like ffurrer2/extract-release-notes to extract release notes from changelogs, that would be easier for GH CLI to create releases.