add BuyCryptoOrder and SellCryptoOrder entities

db/migrate/20210814194513_create_sell_crypto_orders.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+class CreateSellCryptoOrders < ActiveRecord::Migration[6.1]
+  def change
+    create_table(:sell_crypto_orders) do |t|
+      t.references(:user, null: false, foreign_key: true)
+      t.references(:currency, null: false, foreign_key: true)
+
+      t.string(:status, null: false)
+      t.decimal(:paid_amount, precision: 20, scale: 10, null: false, default: 0)
+      t.integer(:received_amount_cents, null: true)
+
+      t.timestamps
+    end
+  end
+end