added create category support

src/app/services/category.service.ts

@@ -17,6 +17,10 @@ export class CategoryService {
     this.internalCategories.set(await this.http.get<Category[]>(this.categoryPath));
   }
 
+  public async createCategory(category: CreateCategory): Promise<Category> {
+    return await this.http.post<Category>(this.categoryPath, category);
+  }
+
   public async updateCategory(category: Category): Promise<Category> {
     return await this.http.put<Category>(this.categoryPath, category);
   }