Add an EFCore MongoDB Test Suite

[adrianhall]

Customer is using MongoDB with EF Core. Need a test suite across both controller and EF Core.

[adrianhall]

Requires a 9.x version of MongoDB.EntityFrameworkCore - see mongodb/mongo-efcore-provider#180

Once available, this can be dealt with.

[adrianhall]

Removing as it is not possible due to transactional requirements in the 9.0.0 release. Will re-visit when someone complains.