In v10 `MultiTenantIdentityDbContext` does not work with attached entities by default

[AndrewTriesToCode]

MultiTenantIdentityDbContext will throw an exception about a non null primary key on the UserLogins table if you use an external login provider.

To workaround this in your MultiTenantIdentityDbContext derived class contructor call EnforceMultiTenantOnTracking.

In the next release this will be added to the base class constructor.