Add changelog entries generation script
What does this MR do?
Adds a script that helps to automatically prepare entries for CHANGELOG.md file.
Script assumes that a GITLAB_PRIVATE_TOKEN is set and it contains users API access token.
If nothing else is set it will find all merge requests from the latest stable tag (a tag with a vX.Y.Z pattern). However there may be a situation (like for v1.6.0 release) that the previous stable tag is created not in the current branch history. In such case the STARTING_POINT may be used to set a SHA which should be used, eg. STARTING_POINT=3e1ec38 ./scripts/prepare-changelog-entries.rb
If there is a MR that was next reverted, we can use the EXCLUDE_MR_IDS variable, eg. EXCLUDE_MR_IDS=123,456,777 ./scripts/prepare-changelog-entries.rb
Why was this MR needed?
While preparing a release process description we've decided that it would be good to automatically generate CHANGELOG entries basing on merge requests titles.