[tracking] Run a local testnet

[MegaRedHand]

• Support loading custom config files from YAML #804
• Add flag to enable metrics endpoint #813
• Load genesis state with custom config #806
• Rename bootnodes.yaml to boot_enr.yaml #807
• Allow specifying DB location #808
• Allow configuring ports used by Libp2p #810
• Allow configuring the port which serves the Beacon API #811
• Add scripts and instructions for setting up/tearing down a local testnet (see [Infra] Create local testnet #172 (comment))

[Arkenan]

Labelling this umbrella ticket under validator as it will unblock testing the message sending as well.