Add sitemap generation for Gitlab.com and gitlab-org namespace [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

In !46661 (merged) we implemented the logic to generate dynamically the sitemap for the gitlab-org namespace and only in Gitlab.com.

The feature flag has been enabled globally for 4-5 months and AFAIK there hasn't been any hiccup. I let the flag for so long because I wanted to be able to turn it off in case something goes wrong.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Related to #276915 (closed)