Add CI workflow to enforce additions in CHANGELOG.md

[taimoorzaeem]

Problem

We often forget to add the entry in CHANGELOG.md at the right spot which then needs to be corrected later as occurred in #4531 and #4589.

Solution

Have a CI workflow to check that on certain commit prefixes like fix: and add:, the CHANGELOG.md should contain the entry/change at the right spot using sed or git commands.