Make it easier to specify which nodes are running validators and which aren't

[Parithosh Jayanthi]

Ideally we can just specify a no_validator_keys and it runs everything except the validator part. this is something we use extensively in testnets and would benefit from some automation.

[Barnabas Busa]

ethereum_node_cl_validator_enabled=false does that. It works on every run (except first one, related issue: #68)