suggestion to optimize workshop start

comments from tartu workshop:

the start of the workshop is quite chaotic, on one hand because some still need to install the docker environment, on the other hand because the initial exercises focus (in my opinion) to much on docker options. My suggestion would be to remove some of those exercises, and jump directly to the use of docker compose.

- Remove the full `Customizing configuration` section
- remove `Adding data and setting the configuration file`
- move `Using Docker for Python Clients` to the relevant owslib section where it is used

- undo the data volume uncomment, do we even mention it in docs still?