allow multiple `--target` url values for failover cases

[rampall]

multiple --target url values pointing to multiple nodes can gracefully handle failover cases when

• a node is waiting to sync
• a node is migrating
• request timed out etc
• out of requests on rate-limited endpoints

[rampall]

Reference: Out of requests error from getblock

2023-10-06T12:09:13: TypeError: Cannot create property 'id' on string 'Out of requests'
2023-10-06T12:09:13: at /home/rp/.nvm/versions/node/v20.8.0/lib/node_modules/etherproxy/dist/utility.js:33:25
2023-10-06T12:09:13: at Generator.next ()
2023-10-06T12:09:13: at fulfilled (/home/rp/.nvm/versions/node/v20.8.0/lib/node_modules/etherproxy/dist/utility.js:5:58)
2023-10-06T12:09:13: at process.processTicksAndRejections (node:internal/process/task_queues:95:5)