SER-1386 add ExtraData and Source GSFs

Summary:
------------------------------
FlexCharge: quick fix on void call

[SER-1386](https://spreedly.atlassian.net/browse/SER-1386)

Remote Test:
------------------------------
Finished in 70.477035 seconds.
19 tests, 54 assertions, 0 failures, 0 errors, 0 pendings,
1 omissions, 0 notifications
100% passed

Unit Tests:
------------------------------
Finished in 124.425603 seconds.
5959 tests, 79971 assertions, 0 failures, 0 errors, 0 pendings,
0 omissions, 0 notifications
100% passed

RuboCop:
------------------------------
798 files inspected, no offenses detected

lib/active_merchant/billing/gateways/flex_charge.rb

@@ -41,6 +41,7 @@ def purchase(money, credit_card, options = {})
         add_address(post, credit_card, address(options))
         add_customer_data(post, options)
         add_three_ds(post, options)
+        add_metadata(post, options)
 
         commit(:purchase, post)
       end
@@ -114,6 +115,11 @@ def inquire(authorization, options = {})
         commit(:inquire, {}, order_id, :get)
       end
 
+      def add_metadata(post, options)
+        post[:Source] = 'Spreedly'
+        post[:ExtraData] = options[:extra_data] if options[:extra_data].present?
+      end
+
       private
 
       def address(options)

test/remote/gateways/remote_flex_charge_test.rb

@@ -26,7 +26,8 @@ def setup
       cvv_result_code: '111',
       cavv_result_code: '111',
       timezone_utc_offset: '-5',
-      billing_address: address.merge(name: 'Cure Tester')
+      billing_address: address.merge(name: 'Cure Tester'),
+      extra_data: { hello: 'world' }.to_json
     }
 
     @cit_options = @options.merge(

test/unit/gateways/flex_charge_test.rb

@@ -25,7 +25,8 @@ def setup
       cavv_result_code: '111',
       timezone_utc_offset: '-5',
       billing_address: address.merge(name: 'Cure Tester'),
-      sense_key: 'abc123'
+      sense_key: 'abc123',
+      extra_data: { hello: 'world' }.to_json
     }
 
     @cit_options = {
@@ -108,6 +109,8 @@ def test_successful_purchase
         assert_equal request['orderId'], @options[:order_id]
         assert_equal request['idempotencyKey'], @options[:idempotency_key]
         assert_equal request['senseKey'], 'abc123'
+        assert_equal request['Source'], 'Spreedly'
+        assert_equal request['ExtraData'], { hello: 'world' }.to_json
         assert_equal request['transaction']['timezoneUtcOffset'], @options[:timezone_utc_offset]
         assert_equal request['transaction']['amount'], @amount
         assert_equal request['transaction']['responseCode'], @options[:response_code]