Add a GitHub Actions workflow to regularly regenerate this page

[fingolfin]

We should regularly "touch" this repository to force GitHub to regenerate http://gap-packages.github.io, so that newly added package repository appear, and meta data changes become visible.

A simple way to ensure that would be to setup a daily Travis cron job, which would check out the repository, and run the force-rebuild.sh script in it. Of course we'd have to add an (encrypted) authorization key into the .travis.yml file to ensure suitable push access.

[wilfwilson]

The website is automatically built and deployed now by a GitHub Actions workflow: see https://github.com/gap-packages/gap-packages.github.io/actions/workflows/pages/pages-build-deployment

This happens whenever there is a push to the master branch of the repository.

However, this is set up automatically by GitHub, and I don't immediately see a way of additionally configuring this script to run on a schedule.

We could try to manually re-construct their Workflow, and keep it up to date, but that seems sub-optimal.