Toggle analytics navbar feature flags default on

What does this MR do?

After testing the feature flags on gitlab.com for a few days we can safely enable them by default. This change also requires documentation update.

• analytics_pages_under_project_analytics_sidebar
• analytics_pages_under_group_analytics_sidebar

The feature flags with the analytics navbar are enabled on PRD:

• Group: gitlab-org
• Project: gitlab

The feature flag will be cleaned up in 12.9. Issue

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content