Update checks for consolidated list

What does this MR do and why?

• Introduces helper methods on the group and project models to easily check whether the consolidated list is enabled or not
• Updates the FF check in numerous places to enable the FF for subgroups if an ancestor has it enabled

References

• #520452
• Current feature flag status (internal)

Screenshots or screen recordings

work_item_planning_view disabled	work_item_planning_view enabled

How to set up and validate locally

1. Ensure the work_item_planning_view feature flag is disabled
2. Navigate to a group and project. Observe that the nav bar on the left has Issues and Epics as options where appropriate
3. Enable work_item_planning_view
4. Navigate to a group and project. Observe that the nav bar on the left has Work Items as options, and selecting these navigates to the consolidated list view

MR acceptance checklist

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