Override about_feature_comparison_url method

What does this MR do and why?

Override about_feature_comparison_url method to https://about.gitlab.cn/pricing/saas/feature-comparison

Screenshots or screen recordings

none

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Closes #2917 (closed)