Begins tracking the given entity, and any other reachable entities that are           not already being tracked, in the Added state such that they will           be inserted into the database when SaveChanges() is called.             Use State to set the state of only a single entity.             This method is async only to allow special value generators, such as the one used by           'Microsoft.EntityFrameworkCore.Metadata.SqlServerValueGenerationStrategy.SequenceHiLo',           to access the database asynchronously. For all other cases the non async method should be used.