bug: Undefined RPC_URL

[merli-eigenlabs]

How to reproduce it:

• Follow the Quick start guide on the README file.
• On the step for running npm run start:operator you'll get the following error:

JsonRpcProvider failed to detect network and cannot start up; retry in 1s (perhaps the URL is wrong or the node is not started)
Error in registering as operator: Error: connect ECONNREFUSED ::1:8545
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1555:16) {
  errno: -61,
  code: 'ECONNREFUSED',
  syscall: 'connect',
  address: '::1',
  port: 8545
}
Error in main function: Error: connect ECONNREFUSED ::1:8545
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1555:16) {
  errno: -61,
  code: 'ECONNREFUSED',
  syscall: 'connect',
  address: '::1',
  port: 8545
}