fix: Update required fields for CreateFile schema object in openapi.yaml

[brendenehlers]

Issue: #1050

Updates the required fields for the CreateFile schema object in the Open API specification.

Minimal request body to create a new file:

{
    "fileHeader": {
        "immediateDestination": "226071004",
        "immediateOrigin": "0462723539",
        "fileCreationDate": "220716"
    },
    "batches": [
        {
            "batchHeader": {
                "serviceClassCode": 220,
                "companyName": "HMBradley",
                "companyIdentification": "0462723539",
                "standardEntryClassCode": "WEB",
                "companyEntryDescription": "HMBWEB",
                "ODFIIdentification": "22607100"
            },
            "entryDetails": [
                {
                    "transactionCode": 22,
                    "RDFIIdentification": "06540013",
                    "checkDigit": "7",
                    "DFIAccountNumber": "264236473264",
                    "amount": 121598,
                    "individualName": "Zach Test"
                }
            ]
        }
    ]
}