Add CircleCI check for changelog format

[timobrembeck]

Motivation

The changelog is parsed by the following dark magic bash command:

integreat-cms/.circleci/config.yml

Line 366 in 9bc0251

CHANGELOG=$(awk -v RS='\n\n\n' 'NR==2 {print $0}' CHANGELOG.md | tail -n +4 | sed --regexp-extended 's|\[#([0-9]+)\]\(https://github\.com/digitalfabrik/integreat-cms/issues/([0-9]+)\)|#\1|')

which requires exactly one line after the version heading and two new lines after the bullet points.

Proposed Solution

Add a script which checks the format in CircleCI

Alternatives

Improve the bash command to handle more changelog formats

Additional Context

[timobrembeck]

It's quite a common problem that the changelog entry does not end up in the unreleased section after rebasing, so we should definitely add a check for this as well.

[david-venhoff]

Not sure if it is worth the effort in our case, but I found this solution interesting where every changelog entry got its own file: https://about.gitlab.com/blog/2018/07/03/solving-gitlabs-changelog-conflict-crisis/

[timobrembeck]

Yes, this is exactly the idea I had in mind when creating #1763.
Also not sure, but if we count all the developer hours which are spent with conflict resolution, maybe it will pay off in the long term 😄