Define query splitting behaviour

[JimKerslake]

To get rid of log warnings

https://learn.microsoft.com/en-us/ef/core/querying/single-split-queries

[JimKerslake]

cloudscribe.SimpleContent.Storage.EFCore.Common 6.0.2
cloudscribe.SimpleContent.Storage.EFCore.MSSQL 6.0.2
cloudscribe.SimpleContent.Storage.EFCore.pgsql 6.0.2
cloudscribe.SimpleContent.Storage.EFCore.PostgreSql 6.0.3

[JimKerslake]

Needs a test that we no longer see the error log messages complaining about the lack of a query splitting strategy.
However those errors can come from anywhere in any assembly that has a DbContext, and this ticket refers only to the simplecontent part of the whole cs stack... there are other places probably still needing this change in other repos. And of course all of the database options that support it. I think I did Core and SimpleContent at least, so far...