Reapply "feat(stats): add user ids to inference metrics"

This reverts commit e0ff4fd1ac.

packages/stats/core/src/domain/inference.ts

@@ -75,6 +75,7 @@ WITH normalized AS (
     session,
     COALESCE(NULLIF(workspace, ''), '') AS workspace,
     COALESCE(NULLIF(api_key, ''), '') AS api_key,
+    COALESCE(NULLIF(user_id, ''), '') AS user_id,
     status,
     duration AS duration_ms,
     time_to_first_byte AS ttfb_ms,
@@ -116,7 +117,7 @@ WITH normalized AS (
     country,
     continent,
     session,
-    COALESCE(NULLIF(workspace, ''), NULLIF(api_key, '')) AS user_key,
+    COALESCE(NULLIF(user_id, ''), NULLIF(workspace, ''), NULLIF(api_key, '')) AS user_key,
     status,
     duration_ms,
     ttfb_ms,