Automatically generate changelog item

As discussed in charts/helm.gitlab.io#276, we should start adding a Changelog item to all changes we create after we announce the Alpha.

We can use the tool we already have in CE.

This tool is currently getting called by the release-tools to collect all generated files to a new release.

We can reuse that and adapt this to our needs.

My suggestion is to:

1. Adopt the use of changelog script for every MR
2. Add a CI job to run in master only. Possibly run on schedule, to add to main changelog

@Ahmadposten @twk3 @WarheadsSE @joshlambert what do you think?