feat: add entity checks in RoCrateBuilder for data and contextual entities

Author: Pfeil

src/main/java/edu/kit/datamanager/ro_crate/RoCrate.java

@@ -375,12 +375,14 @@ public RoCrateBuilder addDescription(String description) {
          * @return returns the builder for further usage.
          */
         public RoCrateBuilder addDataEntity(DataEntity dataEntity) {
+            this.metadataContext.checkEntity(dataEntity);
             this.payload.addDataEntity(dataEntity);
             this.rootDataEntity.addToHasPart(dataEntity.getId());
             return this;
         }
 
         public RoCrateBuilder addContextualEntity(ContextualEntity contextualEntity) {
+            this.metadataContext.checkEntity(contextualEntity);
             this.payload.addContextualEntity(contextualEntity);
             return this;
         }