server: Docker expects to be run from the repository root

Currently, the server docker containers all expect to be run from the mono-repository root: 

```
docker build -t basyx-python-server -f Dockerfile ../../..
```

(where `../../..` is the repository root). 
This functional, but arguably somewhat ugly.

Let's discuss the possibility to change this, for example to the `./server` directory.
Nevertheless, we should research how other projects do this. 