fix(backend): Foute entity-structuur van leerpaden verbeterd.

Ook testen geschreven voor LearningPathRepository en LearningObjectRepository.

backend/src/entities/content/learning-path-transition.entity.ts

@@ -0,0 +1,17 @@
+import {Entity, ManyToOne, PrimaryKey, Property} from "@mikro-orm/core";
+import {LearningPathNode} from "./learning-path-node.entity";
+
+@Entity()
+export class LearningPathTransition {
+    @ManyToOne({entity: () => LearningPathNode })
+    node!: LearningPathNode;
+
+    @PrimaryKey({ type: 'numeric' })
+    transitionNumber!: number;
+
+    @Property({ type: 'string' })
+    condition!: string;
+
+    @ManyToOne({ entity: () => LearningPathNode })
+    next!: LearningPathNode;
+}