feat(03-01): add pgx/v5, PostgreSQL migrations, rename RunMigrations to RunSQLiteMigrations

- Add github.com/jackc/pgx/v5 v5.9.1 dependency
- Add golang-migrate pgx/v5 driver
- Create migrations/postgres/0001_initial_schema.up.sql with SERIAL PRIMARY KEY
- Create migrations/postgres/0001_initial_schema.down.sql
- Rename RunMigrations to RunSQLiteMigrations in migrate.go
- Add RunPostgresMigrations with pgxmigrate driver and 'pgx5' name
- Update export_test.go to use RunSQLiteMigrations (go vet compliance)

pkg/diunwebhook/migrations/postgres/0001_initial_schema.up.sql

@@ -0,0 +1,28 @@
+CREATE TABLE IF NOT EXISTS updates (
+    image           TEXT PRIMARY KEY,
+    diun_version    TEXT NOT NULL DEFAULT '',
+    hostname        TEXT NOT NULL DEFAULT '',
+    status          TEXT NOT NULL DEFAULT '',
+    provider        TEXT NOT NULL DEFAULT '',
+    hub_link        TEXT NOT NULL DEFAULT '',
+    mime_type       TEXT NOT NULL DEFAULT '',
+    digest          TEXT NOT NULL DEFAULT '',
+    created         TEXT NOT NULL DEFAULT '',
+    platform        TEXT NOT NULL DEFAULT '',
+    ctn_name        TEXT NOT NULL DEFAULT '',
+    ctn_id          TEXT NOT NULL DEFAULT '',
+    ctn_state       TEXT NOT NULL DEFAULT '',
+    ctn_status      TEXT NOT NULL DEFAULT '',
+    received_at     TEXT NOT NULL,
+    acknowledged_at TEXT
+);
+
+CREATE TABLE IF NOT EXISTS tags (
+    id   SERIAL PRIMARY KEY,
+    name TEXT NOT NULL UNIQUE
+);
+
+CREATE TABLE IF NOT EXISTS tag_assignments (
+    image  TEXT PRIMARY KEY,
+    tag_id INTEGER NOT NULL REFERENCES tags(id) ON DELETE CASCADE
+);