adjust pipeline: build and deploy every week
Until now, the website is built and deployed at every commit to the main branch.
Additionally it is necessary to build and deploy the website once in a set time interval regardless of the commits to the main branch. The reason for that is that there might be pages with an expiry date. If a page is expired it will not be considered in the website building process. However, this expiration will only be noticed at the time the website is built. Therefore, the website needs to be built on a regular basis.