feat: add premium tiers table

Author: manuelsc

backend/pkg/commons/db/migrations/postgres/20250819120437_premium_tiers.sql

@@ -0,0 +1,17 @@
+-- +goose Up
+-- +goose StatementBegin
+
+CREATE TABLE IF NOT EXISTS premium_tiers (
+    purchase_id VARCHAR(255) NOT NULL,
+    tier_id VARCHAR(255) NOT NULL,
+    PRIMARY KEY (purchase_id)
+);
+
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+
+DROP TABLE IF EXISTS premium_tiers;
+
+-- +goose StatementEnd