db: add migration to create subscription_tokens table

Author: alexsavio

migrations/20240403111912_create_subscription_tokens_table.sql

@@ -0,0 +1,7 @@
+-- Add migration script here
+
+CREATE TABLE subscription_tokens (
+    subscription_token TEXT NOT NULL,
+    subscriber_id UUID NOT NULL REFERENCES subscriptions (id),
+    PRIMARY KEY (subscription_token)
+);