Update product analytics docs with changelog for permissions

What does this MR do and why?

Adds an item to the docs specifying when permissions for product analytics onboarding were updated.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

docs only change

How to set up and validate locally

View updated docs:

http://gdk.test:3005/ee/user/product_analytics#onboard-a-gitlab-project

Related to #465414 (closed)