Create type discount_usage (#476)

* Create type discount_usage

* Add discount_codes.discount_usage_type

* Fix SQL

* Make query idempotent

* Bump revision

migrations/000.553.sql

@@ -0,0 +1,14 @@
+ALTER TABLE discount_codes
+ DROP COLUMN IF EXISTS discount_usage_type;
+
+DROP TYPE IF EXISTS discount_usage;
+
+CREATE TYPE discount_usage AS ENUM (
+    'default',
+    'influencer',
+    'customer service',
+    'internal'
+);
+
+ALTER TABLE discount_codes
+  ADD COLUMN discount_usage_type discount_usage NOT NULL DEFAULT 'default';