Add support for local config

[nikita-kotsehub]

1. As of now, the central server needs to know the location of the local data, which is not privacy-preserving and adds a dependency
2. Instead, we can either
   1. provide a configuration file with that info (maybe such that FLoX reaches out to the devices and asks for the file first)
   2. or have the devices just pull the info from configuration files locally