fix(openapi): use snake_case when generating OpenAPI schema

[fadeev]

Description

Configure OpenAPI to output field names that match what's returned by the actual API.

Expected:

{
  "CrossChainTx": [
    {
      "creator": "zeta18pksjzclks34qkqyaahf2rakss80mnusju77cm",
      "index": "0x0e7627335d1ca4422b8171288741403792626448da268d6902e6dc3a921fbd79",
      "zeta_fees": "0",
      "relayed_message": "",
      "cctx_status": {
        "status": "OutboundMined",
        "status_message": "First half of EVM transfer Completed",
        "lastUpdate_timestamp": "1686603271"
      },
      "inbound_tx_params": {
        "sender": "0x6dA30bFA65E85a16b05bCE3846339ed2BC746316",
        "sender_chain_id": "5",
        "tx_origin": "0x6dA30bFA65E85a16b05bCE3846339ed2BC746316",
        "coin_type": "Gas",
        "asset": "",
        "amount": "100000000000000000",
        "inbound_tx_observed_hash": "0x71d493c395606050a75c79328a9a77c10bc92a7be144655c153fe7a7954b4e84",
        "inbound_tx_observed_external_height": "9168040",
        "inbound_tx_ballot_index": "0x0e7627335d1ca4422b8171288741403792626448da268d6902e6dc3a921fbd79",
        "inbound_tx_finalized_zeta_height": "0"
      },
      "outbound_tx_params": [
        {
          "receiver": "0x6dA30bFA65E85a16b05bCE3846339ed2BC746316",
          "receiver_chainId": "7001",
          "coin_type": "Gas",
          "amount": "0",
          "outbound_tx_tss_nonce": "0",
          "outbound_tx_gas_limit": "90000",
          "outbound_tx_gas_price": "",
          "outbound_tx_hash": "",
          "outbound_tx_ballot_index": "",
          "outbound_tx_observed_external_height": "0"
        }
      ]
    }
  ],
  "pagination": {
    "next_key": "MHgxOWY0NTVkYjNhNGU3MWQ0MWM5ZGFjNTgzYzY5Y2Q4MDU1NWUxZGM0OWI2NDZmOGMwZDVkMjA5NTcwM2Y3YWYw",
    "total": "0"
  }
}

Source: https://zetachain-testnet.nodejumper.io:1317/zeta-chain/crosschain/cctx?pagination.limit=1

Before the fix:

After the fix:

To check it out, run:

go run docs/main.go

Details:

https://grpc-ecosystem.github.io/grpc-gateway/docs/development/grpc-gateway_v2_migration_guide/#we-now-use-the-camelcase-json-names-by-default

Context:

https://zetachain.slack.com/archives/C0263N9EKL6/p1686676457123299

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation updat

[brewmaster012]

Ship it!