Allow setting the migration type name

Author: ejsmith

src/Foundatio.Repositories.Elasticsearch/Repositories/MigrationsRepository.cs

@@ -7,6 +7,6 @@ public MigrationRepository(IIndexType<Migration> indexType) : base(indexType) {}
     }
 
     public sealed class MigrationType : DynamicIndexType<Migration> {
-        public MigrationType(IIndex index) : base(index) {}
+        public MigrationType(IIndex index, string name = "migration") : base(index, name) {}
     }
 }