Add rake tasks for alternative way to specify Changelog entries

[ydah]

Follow: rubocop/rubocop#8930 and rubocop/rubocop-rails#496

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• [-] Updated documentation.
• [-] Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[pirj]

I feel severe reluctance to this approach. We don't have that many updates, and rebasing and fixing the changelog doesn't feel to be a significant overhead. Contrary to a strict suggested format.

The changelog file in between the releases is also now scattered across several files.

I hope that with splitting the repo, the surface will reduce as well.

During a few recent minor releases, we were doing a good job of communicating on PRs and merged them quickly.

[ydah]

• Move towards changelog generation #1417

It was spoken about here, so we worked on it. However, it is true that we don't get that many PRs sent to us on a daily basis now, so it may just be overhead.
Basically this approach is the same as rubocop and rubocop-rails, so we can always come back to this.

[pirj]

My apologies. I refreshed my memory by reading #1417 and now recall I gave in, provided all the arguments, but kept my previous opinion.
Thanks for this PR.
I would personally postpone the decision until the need arises.

[ydah]

We can resume this again, so let's Close this PR.