IdStory Identity Manager

We should check the transaction isolation levels when using MSSQL. It might be a reason for some duplicate role assignments that we encountered during testing.
Reading: https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/sql/snapshot-isolation-in-sql-server .

The catch here is that setting READ_COMMITTED_SNAPSHOT=ON basically enables per-transaction row versioning. Although the error should be raised when such transactions modify the same data, I do not know how this applies to non-conflicting INSERT statements on the same table. In theory, it may be possible for two IdM transactions to read the same data, infer the same result and ultimately insert the same data rows into a table. Example: user from GUI doing re-save on identity and some scheduled task running in the background retrying failed events. (It is a long stretch, I know. But we still we should check this; better safe than sorry.)

Ondra: please assign to somebody and to some product version.