Product analytics graphs page

What does this MR do?

Add graphs page to Product Analytics feature. The goal of this page is to show some basic data and be a foundation for a customized user dashboard in future.

Notes:

1. Last part of Product Analytics feature MVP #225167 (closed)
2. The feature itself is behind feature flag and is disabled by default.
3. Thanks @wortschi for making the frontend code.
4. Documentation was mostly done in !36443 (merged) and will be improved further in #232495 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

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