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

db/migrate/20220623113405_add_parent_id_to_category.rb

@@ -0,0 +1,5 @@
+class AddParentIdToCategory < ActiveRecord::Migration[6.1]
+  def change
+    add_reference :categories, :parent_category, foreign_key: { to_table: :categories }
+  end
+end

db/migrate/20220623113604_create_related_categories.rb

@@ -0,0 +1,12 @@
+class CreateRelatedCategories < ActiveRecord::Migration[6.1]
+  def change
+    create_table :related_categories do |t|
+      t.bigint :category_id
+      t.bigint :related_category_id
+      t.timestamps
+    end
+
+    add_index :related_categories, [:category_id, :related_category_id], unique: true
+    add_index :related_categories, [:related_category_id, :category_id], unique: true
+  end
+end

db/migrate/20220627135753_add_linked_category_id_to_categories.rb

@@ -0,0 +1,5 @@
+class AddLinkedCategoryIdToCategories < ActiveRecord::Migration[6.1]
+  def change
+    add_reference :categories, :linked_category, foreign_key: { to_table: :categories }
+  end
+end