message: refactor(docs-infra): change class to interface where class properties not used
  In resource.model.ts the interfaces of the resources were defined as classes, these do not use any class properties and are only used for type checking. So, changed them from class to interface.
  PR Close
diff: -export class Category {
  +export interface Category {
  id: string; // "education"
  title: string; // "Education"
  order: number; // 2
  subCategories: SubCategory[];
  }
  -export class SubCategory {
  +export interface SubCategory {
  id: string; // "books"
  title: string; // "Books"
  order: number; // 1
  resources: Resource[];
  }
  -export class Resource {
  +export interface Resource {
  category: string; // "Education"
  subCategory: string; // "Books"
  id: string; // "-KLI8vJ0ZkvWhqPembZ7"
  