Update redirect file end date

doc/development/product_analytics/index.md

@@ -4,5 +4,10 @@ redirect_to: 'https://about.gitlab.com/handbook/product/product-analytics-guide/
 
 This document was moved to [another location](https://about.gitlab.com/handbook/product/product-analytics-guide/).
 
-<!-- This redirect file can be deleted after February 1, 2021. -->
+<!-- Needed by the Product Intelligence group
+
+Since our new standard for redirects otherwise lies within the gitlab-docs repo,
+as long as we need a redirect to the handbook, we need to retain this file.
+ -->
+<!-- This redirect file can be deleted after December 1, 2021. -->
 <!-- Before deletion, see: https://docs.gitlab.com/ee/development/documentation/#move-or-rename-a-page -->