nodebuilder/p2p: Consider redesign of network determination/configuration

[Wondertan]

Currently, we only have vars defined in ‘params’

Consider redesigning the network determination/configuration functionality since it is split between parsing env for custom network vs using --p2p.network to choose from a select amount of (valid) networks and it is confusing especially for those who rely on this functionality for testing / spinning up custom networks.

[Bidon15]

Grooming 16/11/2022:

Moving to post-mainnet