feat(backend): Databank initialiseren

Verbinding met databank aangemaakt, eerste entities toegevoegd, centrale API aangemaakt om omgevingsvariabelen voor onze app op te vragen.

backend/src/entities/users/student.entity.ts

@@ -0,0 +1,6 @@
+import {User} from "./user.entity";
+import { Entity } from '@mikro-orm/core';
+
+@Entity()
+export class Student extends User {
+}

backend/src/entities/users/teacher.entity.ts

@@ -0,0 +1,7 @@
+import { Entity } from '@mikro-orm/core';
+import {User} from "./user.entity";
+
+@Entity()
+export class Teacher extends User {
+
+}

backend/src/entities/users/user.entity.ts

@@ -1,9 +1,9 @@
 import { Entity, PrimaryKey, Property } from '@mikro-orm/core';
 
-@Entity()
+@Entity({abstract: true})
 export class User {
-    @PrimaryKey({ type: 'number' })
-    id!: number;
+    @PrimaryKey({type: "string"})
+    username!: string;
 
     @Property()
     firstName: string = '';