Add ability to ensure ef core context interface and implementation match

[fb-smit]

We should add a method in the testing project which enables to check if the interface is missing any public DbSet<> from the acutal context class.

Check could look something like this

var interfacesSets = typeof(IMyDBContext).GetProperties().Select(x => x.Name);
var implementationSets = typeof(MyDBContext)
    .GetProperties(BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.Public)
    .Select(x => x.Name);
string.Join(' ', implementationSets.Except(interfacesSets)).Should().BeEmpty();

The assert statement also has the benefit of showing the actual missing DbSet<> names, so one can add them easily