Add sample CHANGELOG and changelog generation/update script

[iajoiner]

Description

Add a sample CHANGELOG.md as well as the script that generates/updates CHANGELOG.md and CHANGELOG-old.md

Closes #996.

Features:

1. Contributions with the label "dependencies" which are abundant, are always made by dependabot and are not very useful in a changelog have been ignored.
2. Ignore tags with different languages (e.g. ignore any Python tag when producing the changelog from Rust 0.5.0 to Rust 0.6.0).

Features in future PRs:

1. Filter out contributions that are from unrelated languages which will probably benefit from autolabelling of PRs.

[roeap]

Really looking forward to doing more frequent, higher quality releases :), thanks!

You would have to rebase or merge once for me to trigger CI.

[roeap]

@iajoiner - i was about to merge this, when i realized this would bump the rust version to 0.6.0 create the changlog for yet unreleased 0.6.0. Is this intentional? And if so, would the script update the log once we do the actual release?

[iajoiner]

@roeap This is really just a preview of what will happen once we do actually have a release. However we do need to add historical changelogs. In order for Python changes between a Python release and the Rust release after that to not be included into the Rust release and vice versa we need to get PR autolabeling done first.

[roeap]

makes sense :) - i took the liberty to convert this to draft, hope that is OK.

[iajoiner]

Once #1030 is merged I will improve this one.