Prepare an integrator approval transaction for L1 signing

Signs the approve-integrator transaction with backend-configured fee parameters and returns a message for the frontend to sign with the L1 wallet

curl -X POST "https://example.com/misc/lighter/prepare-approve-integrator" \  -H "Content-Type: application/json" \  -d '{    "accountIndex": 0,    "apiKeyIndex": 0,    "apiPrivateKey": "string"  }'

{  "messageToSign": "string",  "txInfo": "string"}