Move Productivity Analytics to the group level

What does this MR do?

This change removes the Productivity Analytics navbar item from the Analytics namespace and moves it under the Group level. The change is behind a global feature flag.

Note: there is a bit of code duplication due to the move of PA. Reusing the existing controllers was not possible (will be cleaned up when the FF is eliminated: 12.9).

• ee/app/controllers/analytics/productivity_analytics_controller.rb -> ee/app/controllers/groups/analytics/productivity_analytics_controller.rb
• ee/spec/controllers/analytics/productivity_analytics_controller_spec.rb -> spec/controllers/groups/analytics/productivity_analytics_controller_spec.rb

A follow-up MR will take care of toggling the FF default on and update the docs (12.8).

Note: to test this feature, two FFs must be enabled:

• analytics_pages_under_group_analytics_sidebar
• group_level_productivity_analytics

Screenshots

Before

After

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

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team