changed DocumentArray discriminator to allow recieving both document and model templates

types/mongoose/index.d.ts

@@ -2409,6 +2409,13 @@ declare module "mongoose" {
          */
         discriminator<U extends Document>(name: string, schema: Schema): Model<U>;
 
+        /**
+         * Adds a discriminator type.
+         * @param name discriminator model name
+         * @param schema discriminator model schema
+         */
+        discriminator<U extends Document, M extends Model<U>>(name: string, schema: Schema): M;
+
       }
 
       /*