[BB-5138] Improve docs
Description
This MR adds documentation about Grove's way of configuration and configuration override. Also, rearrange some docs to appropriate places.
Supporting information
https://tasks.opencraft.com/browse/BB-5138
Testing instructions
- Pull this MR.
- Install docs requirements
pip install -r requirements.docs.txt
. - Serve docs
mkdocs serve
. - Check the changes.