Convention to ignore extra properties should be set automatically

[einari]

We don't always want to map all the properties in a Document. By default, the serializer should ignore properties that are not on the read model.

┆Issue is synchronized with this Asana task

[smithmx]

var pack = new ConventionPack();
pack.Add(new IgnoreExtraElementsConvention(true));
ConventionRegistry.Register("Dolittle Conventions", pack, t => true);