Split configuration according to modules

[mycognosist]

See aquadoggo for a nice pattern, where module-level config is neatly separated and combined into a top-level configuration object: https://github.com/p2panda/aquadoggo/blob/main/aquadoggo/src/config.rs

So we should end up with NetworkConfiguration, JsonRpcConfiguration, MuxRpcConfiguration and ReplicationConfiguration.

This should also help with #24

[mycognosist]

Make sure to implement a validate() method for the Cli struct.

[mycognosist]

Done.