Add Yanwei as autoscaling approver (knative#10250)

Yanwei has been a contributor to Knative from the very beginning, with
first PR going in February 2018. He contributed to various pieces of
autoscaling code including metrics, scraping and autoscaler scaleout.

- Contributor over 3 mo: ✅
- Primary reviewer for at least 10 substantial PRs to the codebase: ✅
(30 L:
https://github.com/knative/serving/pulls?q=is%3Apr+reviewed-by%3Ayanweiguo+is%3Aclosed++label%3Aarea%2Fautoscale+++-author%3Ayanweiguo+label%3Asize%2FL+
+ XL and XXL code reviews)
- Reviewed at least 30 PRs to the codebase: ✅ (77
https://github.com/knative/serving/pulls?q=is%3Apr+reviewed-by%3Ayanweiguo+is%3Aclosed++label%3Aarea%2Fautoscale+++-author%3Ayanweiguo+)

Also 43 contributed merged PRs.

Nominated by an a WG lead: vagababov.

Author: vagababov

Diff for: OWNERS_ALIASES

@@ -40,9 +40,10 @@ aliases:
   - vagababov       # Scaling
 
   autoscaling-approvers:
+  - julz
   - markusthoemmes
   - vagababov
-  - julz
+  - yanweiguo
   autoscaling-reviewers:
   - julz
   - markusthoemmes