Automatically generate a changelog

[louise-davies]

Description:
We'd like to keep a changelog without having to manually update it. This tool: https://github.com/github-changelog-generator/github-changelog-generator seems to work well, and there's a Github Action for it: https://github.com/marketplace/actions/generate-changelog. It would be nice to have a workflow to automate the maintenance of the changelog

Acceptance criteria:

• Automate the changelog maintenance