add roles to admin panel

db/migrate/20220721133421_create_join_table_user_role.rb

@@ -0,0 +1,8 @@
+class CreateJoinTableUserRole < ActiveRecord::Migration[7.0]
+  def change
+    create_join_table(:users, :roles, unique: true) do |t|
+      t.index(%i[user_id role_id])
+      t.index(%i[role_id user_id])
+    end
+  end
+end