[Infra] Create local testnet

[Arkenan]

We should have a docker-compose that allows us to have a local testnet, with an already working full node (e.g. prysm+geth) and a testing full node (e.g. lambda ethereum consensus + reth), with an empty blockchain. This would allow us to quickly test gossiping, propagation of blocks, and others in a controlled manner, and with low resources (i.e. we won't need to save the 2TB full mainnet blockchain locally). While this is not a full-proof method, it allows us to iterate quickly and is perfectly valid to test integrations.

[MegaRedHand]

We can modify these scripts from lighthouse to run our nodes instead. Some things to consider:

• we'll need to add some new flags to our implementation (mainly set port in P2P/HTTP and import initial data from some dir)
• they require installing some external tools (lighthouse, geth, and GNU grep+sed when on mac)

[MegaRedHand]

Expanding on this, we'd need to add the following functionality:

• import a genesis state (which corresponds to phase0) and update it to the latest spec
• flags to set all ports (P2P, discovery, Beacon API)
• load a custom config from a yaml