Obtains block hash by given block height

### Request

```json
{
  "jsonrpc": "2.0",
  "id": 0,
  "method": "on_getblockhash",
  "params": [2111]
}
```

---

### Response

```json
{
  "id": "0",
  "jsonrpc": "2.0",
  "result": "68b3bcf941431fe76420059ce3104bb34ee122a49d0b541af1041ab06e0015bb"
}
```
