feat: Category API to handle linked categories and parent-sub categories (#4879)

app/models/related_category.rb

@@ -0,0 +1,19 @@
+# == Schema Information
+#
+# Table name: related_categories
+#
+#  id                 :bigint           not null, primary key
+#  created_at         :datetime         not null
+#  updated_at         :datetime         not null
+#  category_id        :bigint
+#  related_category_id :bigint
+#
+# Indexes
+#
+#  index_related_categories_on_category_id_and_related_category_id  (category_id,related_category_id) UNIQUE
+#  index_related_categories_on_related_category_id_and_category_id  (related_category_id,category_id) UNIQUE
+#
+class RelatedCategory < ApplicationRecord
+  belongs_to :related_category, class_name: 'Category'
+  belongs_to :category, class_name: 'Category'
+end