add createDepositOrder mutation

app/graphql/mutations/create_deposit_order.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+module Mutations
+  class CreateDepositOrder < BaseMutation
+    field :order, Types::DepositOrderType, null: true
+
+    argument :order, Inputs::CreateStakeOrderAttributesInput, required: true
+
+    def resolve(order:)
+      ActiveRecord::Base.transaction do
+        record = BuildDepositOrder.new(paid_amount_cents: order[:amount_cents], user: current_user.id)
+        record.save!
+
+        { order: record }
+      rescue ActiveRecord::RecordInvalid => e
+        { errors: Resolvers::ModelErrors.from_active_record_model(e.record) }
+      end
+    end
+  end
+end