Add sane configuration values for batch calls

[m-Peter]

curl -XPOST https://previewnet.evm.nodes.onflow.org --header 'Content-Type: application/json' --data-raw '[{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1},{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":2}]' | jq

[
  {
    "jsonrpc": "2.0",
    "id": 1,
    "result": "0xabf"
  },
  {
    "jsonrpc": "2.0",
    "id": 2,
    "result": "0x286"
  }
]

The gateway supports out of the box batch calls (it comes from re-using the original server implementation). This is quite a handy feature, that can save bandwidth. But for production, we would also want to add some sane config values, regarding maximum number of calls and maximum response length, to avoid any performance issues.