Run single Lodestar beacon node

[nflaig]

Right now it's not possible to run just a single Lodestar beacon node without passing additional params

This configuration works

participants:
  - el_type: geth
    el_image: ethereum/client-go:stable
    cl_type: lodestar
    cl_image: chainsafe/lodestar:next
    cl_extra_params:
      - --sync.isSingleNode
      - --network.allowPublishToZeroPeers
    vc_type: teku
    vc_image: consensys/teku:latest
    count: 1

But would it be possible to detect if there is just one node (participant) and automatically set the cl_extra_params as in the provided config?