Add to EC entrypoint a new `case` for multicaster

[pablomendezroyo]

Add on every EC a new case for the multicaster

"multicaster.dnp.dappnode.eth")
  echo "Using multicaster.dnp.dappnode.eth"
  JWT_PATH="/security/multicaster/jwtsecret.hex"
  ;;

Ref: https://github.com/dappnode/DAppNodePackage-geth/blob/faa36c570772a2e1161a0cc7ef0139d0966a02db/entrypoint.sh#L20

[dsimog01]

Nice idea! That would save time in the future