[streamable/brokernode] Node discovery

[CKH4]

How will nodes be discovered?

Suggested readings:
https://medium.com/deviota/carriota-nelson-automatic-peer-discovery-for-iota-bdca9b8b8750
https://github.com/SemkoDev/nelson.cli
https://medium.com/deviota/carriota-nelson-in-a-nutshell-1ee5317d8f19