Staff info is using createdAt field to store owner's name

Overview:
Steps to Reproduce:

1. Create fee/fine
2. Navigate to fee/fine details page
3. Create staff info

Expected Results:

Service point ID should be stored in feefineaction's createdAt field.

Actual Results:

Owner's name is written to createdAt field. Example:

{
  "dateAction" : "2021-07-19T08:56:47.000+00:00",
  "typeAction" : "Staff info only",
  "comments" : "STAFF : Info for staff",
  "amountAction" : 0.0,
  "balance" : 86.0,
  "transactionInformation" : "",
  "createdAt" : "test-owner",
  "source" : "ADMINISTRATOR, DIKU",
  "accountId" : "2a53c7fe-0797-485c-801f-2aee8ed9ab4e",
  "userId" : "2205005b-ca51-4a04-87fd-938eefa8f6de",
  "id" : "57c3e9f8-6c54-49d5-a83c-beaf52340aee"
}

Additional Information:

This bug is affecting other parts of fee/fine functionality:

1. UUID validation is being added to the ID fields in all mod-feesfines JSON schemas (MODFEE-98). It can't be added to createdAt field currently because Staff info functionality will stop working.
2. Financial transactions details report (MODFEE-179) supports filtering by service point (createdAt field). Obviously, it can't filter Staff info records correctly.

What makes this bug even worse, it's unclear what should be done about the historical data that's already stored in the database.