[Bug] add gas used for txns

[antonyip]

This is from chainwalkers.prod.harmony_txs

1. Extract out cumulativeGasUsed as gas_used and convert it into integer for the stg_txs table,
2. Add gas_used to txs table

   {
   "bech32_from": "one17q49nlt0kq6wq87ex8ymm0adr9cnfqnw7w79xv",
   "bech32_to": "one10zuhn4ff2ps7k697xy6czjmggenkzxd0fgmhrq",
   "block_hash": "0xf022ad7d86be3c21f43c3b9f9beac78bcfc9130e58d542e769abe8818fd9a7ac",
   "block_number": 20262462,
   "from": "0xf02a59fd6fb034e01fd931c9bdbfad197134826e",
   "gas": 50000,
   "gas_price": 150000000000,
   "hash": "0x292a2ad9a59da2928c0982b7a43336d4e69330121220028da1afb27711e5e3f6",
   "input": "0x",
   "nonce": "0x65351",
   "r": "0xe87807e23155ebe50b72eb6846b1e5406aa9609debb43390cd889e4a53e7823e",
   "receipt": {
     "bech32_from": "one17q49nlt0kq6wq87ex8ymm0adr9cnfqnw7w79xv",
     "bech32_to": "one10zuhn4ff2ps7k697xy6czjmggenkzxd0fgmhrq",
     "blockHash": "0xf022ad7d86be3c21f43c3b9f9beac78bcfc9130e58d542e769abe8818fd9a7ac",
     "blockNumber": "0x1352e3e",
     "contractAddress": "",
     "cumulativeGasUsed": "0x5208",
     "from": "0xf02a59fd6fb034e01fd931c9bdbfad197134826e",
     "logs": [],
     "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
     "status": "0x1",
     "to": "0x78b979d5295061eb68be3135814b6846676119af",
     "transactionHash": "0x292a2ad9a59da2928c0982b7a43336d4e69330121220028da1afb27711e5e3f6",
     "transactionIndex": "0x0"
   },
   "s": "0x5725df61d1ac05e4dd7c798b86037c448cc19e384750ebb5e48130b0688db658",
   "to": "0x78b979d5295061eb68be3135814b6846676119af",
   "transactionIndex": 0,
   "v": "0x26",
   "value": 107290600000000000000
   }