* Introduce new AuditEntryService
- Moved logic related to the IAuditEntryRepository from the AuditService to the new service
- Introduced new Async methods
- Using ids (for easier transition from the previous Write method)
- Using keys
- Moved and updated integration tests related to the audit entries to a new test class `AuditEntryServiceTests`
- Added unit tests class `AuditEntryServiceTests` and added a few unit tests
- Added migration to add columns for `performingUserKey` and `affectedUserKey` and convert existing user ids
- Adjusted usages of the old AuditService.Write method to use the new one (mostly notification handlers)
* Apply suggestions from code review
* Small improvement
* Some adjustments following code review. Removed UnknownUserKey and used null instead.
* Small adjustments
* Better handle audits performed during the migration state
* Update TODO comment
7fc2bc84de