Allow to add custom prefix on building FAIM file

[chanhengseang3]

In specific use case we want to add some specific string at the beginning of the file.
For example Fiserv Wire file require to start with string "YFT811 ".

My suggestion is to allow to add this through query param. Ex:

curl --request POST \
  --url http://{{host}}/files/create?prefix='YFT811 ' \
  --header 'Content-Type: application/json' \
  --header 'User-Agent: insomnia/10.3.0' \
  --data '{
	"fedWireMessage": {
		"senderSupplied": {
			"formatVersion": "30",
			"userRequestCorrelation": "00000001",
			"testProductionCode": "P",
			"messageDuplicationCode": " "
		},
		"typeSubType": {
			"typeCode": "10",
			"subTypeCode": "00"
		},
		"inputMessageAccountabilityData": {
			"inputCycleDate": "20250113",
			"inputSource": "MBANQ001",
			"inputSequenceNumber": "000004"
		},
		"amount": {
			"amount": "000000000500"
		},
		"senderDepositoryInstitution": {
			"senderABANumber": "121182904",
			"senderShortName": "NORTH BAY CREDIT U"
		},
		"receiverDepositoryInstitution": {
			"receiverABANumber": "121182904",
			"receiverShortName": "NORTH BAY CREDIT U"
		},
		"businessFunctionCode": {
			"businessFunctionCode": "CTR"
		},
		"senderReference": {
      "senderReference": "Generate By SLS UUID"
    },
		"beneficiary": {
			"personal": {
				"identificationCode": "D",
				"identifier": "211432542429",
				"name": "Sai Vatsavai",
				"address": {
					"addressLineOne": "18708 126th Ave NE",
					"addressLineTwo": "Bothell Washington 98011"
				}
			}
		},
		"originator": {
			"personal": {
				"identificationCode": "D",
				"identifier": "360103000879365",
				"name": "Sai Vatsavai",
				"address": {
					"addressLineOne": "18708 126th Ave NE",
					"addressLineThree": "BOTHELL WA 98011"
				}
			}
		},
		"originatorToBeneficiary": {
			"lineOne": "FROM USER"
		}
	}
}'