[OpenSlides] No more update to 3.4 and higher versions possible with the instructions in the Lab

[linux-lukas]

Upon asking in the OpenSlides discussion area in the OpenSlides repo (https://github.com/OpenSlides/OpenSlides/discussions/6283), this became apparent.

Especially for this case, where everything has to be realised manually on the Uberspace, an automatic script that runs through would make a lot of sense.

[linux-lukas]

PR: https://github.com/Uberspace/lab/pull/1142

[luto]

Will version 3.x still receive updates or is it a dead branch now? If 4.x only works using docker, we'll have to remove this guide entirely, sadly :/