CI: Move `publish_documentation` to the beginning of the master pipeline

The master pipeline is interruptible. However, it is quite slow: it runs in ~1h. When the marge-bot pipeline is full, MRs are merged every ~30 minutes. Consequently, each master pipeline is interrupted and documentation is not being published until the marge-bot queue is empty (see screenshot).

A quick fix is to move the publish_documentation to the front of the pipeline. As this job runs in 20 minutes, it should suffice to run one publish per merge on master.