feat(backend): Entities toegevoegd

Entites Class, Class Join Request, Class Invitation, Assignment, Group en entities om de Dwengo-leerinhoud te modelleren, toegevoegd.

backend/src/entities/classes/class-join-request.entity.ts

@@ -0,0 +1,21 @@
+import {Entity, Enum, ManyToOne} from "@mikro-orm/core";
+import {Student} from "../users/student.entity";
+import {Class} from "./class.entity";
+
+@Entity()
+export class ClassJoinRequest {
+    @ManyToOne({entity: () => Student, primary: true})
+    requester!: Student;
+
+    @ManyToOne({entity: () => Class, primary: true})
+    class!: Class;
+
+    @Enum(() => ClassJoinRequestStatus)
+    status!: ClassJoinRequestStatus;
+}
+
+export enum ClassJoinRequestStatus {
+    Open = "open",
+    Accepted = "accepted",
+    Declined = "declined"
+}