Introduce a standard way to deal with changelogs

[maht0rz]

One of the options is to use commitizen and autogenerate changelogs from commits. Additionally we could also squash PRs into a single merge commit + enforce the PR title to satisfy commitizen (there are GH actions for this available).

[rpanic]

We should adhere to Mina's de-facto standard used in o1js, mina-rust, ...
https://keepachangelog.com/en/1.0.0/
This should be tightly integrated with #337