feat(db): add postgresql support

internal/assets/migrations/postgres/000002_oauth_name.up.sql

@@ -0,0 +1,9 @@
+ALTER TABLE "sessions" ADD COLUMN "oauth_name" TEXT NOT NULL DEFAULT '';
+
+UPDATE "sessions"
+SET "oauth_name" = CASE
+  WHEN LOWER("provider") = 'github' THEN 'GitHub'
+  WHEN LOWER("provider") = 'google' THEN 'Google'
+  ELSE UPPER(SUBSTR("provider", 1, 1)) || SUBSTR("provider", 2)
+END
+WHERE "oauth_name" = '' AND "provider" IS NOT NULL;