Enable per node validator count override

[barnabasbusa]

In order to be able to test larger testnets, with more nodes, it is essential to enable local per node validator override.
For example:

{
  "participants": [
    {
      "el_client_type": "geth",
      "cl_client_type": "lighthouse",
    },
    {
      "el_client_type": "geth",
      "cl_client_type": "teku",
      "validator_keys": 1000
    },
  ],
  "network_params": {
    "preregistered_validator_keys_mnemonic": "giant issue aisle success illegal bike spike question tent bar rely arctic volcano long crawl hungry vocal artwork sniff fantasy very lucky have athlete",
    "num_validator_keys_per_node": 64,
    "network_id": "3151908",
    "deposit_contract_address": "0x4242424242424242424242424242424242424242",
    "seconds_per_slot": 12,
    "genesis_delay": 120,
    "capella_fork_epoch": 5,
    "deneb_fork_epoch": 500
  },
  "global_client_log_level": "info"
}

It should create a validator keystore 0-63 for geth-lighthouse and 64-1063 for geth-teku.

[gbouv]

@barnabasbusa do you have cycles to do this?

[barnabasbusa]

Probably not this week. Possibly next week, but thats also not certain yet.