Configure Document Types on whether or not they are multi-tenanted

[jeremydmiller]

In the "multi tenancy by tenant id" approach, let's allow users one way or another to choose which document types should be multi-tenanted.

The config options could be some combination of:

• Policy that says that all documents are multi-tenanted
• Policy that blacklists types that can't be multi-tenanted
• Policy that whitelists types that can't be multi-tenanted
• All users to use Func<Type, bool> filters on what should or should not be multi-tenanted
• Inevitably allow attributes, but that's just a usage of the above bullet.
• Explicitly configure in the Schema.For fluent interface

Much of this depends on #751 being done, but that's relatively small