Add a deploy CI

[berkes]

Maybe just a simple GH actions building the artifacts and another action pushing them to releases. Again another action to push a release to the server.

We hardly have tests. Let alone integration and acceptance tests, so running those is for another issue.

[berkes]

We now have a CI that tests, builds and creates a release. We also have a workflow that is triggered on publishing a release. But somehow this is not triggered.

TODO:

• [x] ensure the deploy workflow gets triggered on publishing a release.
• [x] ensure this workflow can download binary asset from the release (in there, just not tested yet)
• [x] ensure this workflow then uploads that binary using rsync to the server (in there, not tested)
• [x] ensure the workflow then restarts the systemd service (command in makefile)
• [x] doublecheck if rsync works, or if we have to do the scp/mv tango like in the makefile.
• [x] fetch the zipped web assets from release.
• [x] upload them using rsync to the server (and possibly first or later unzip them, but it seems the rsync action already supports this)