Change epic work items rollout per root-group

Enable epic work items rollout from team member... (#471825 - closed) Allowed us to rollout epic work items for a specific group and all its sub-groups, and only enable it for specific users. However, we want to use a percentage actor-based rollout on SaaS where the experience within a group must be the same.

To achieve this we need to the following changes:

• Change work_item_epics feature flag to only check for the root ancestor

To be able to fully rollout to SaaS we need to: remove (or default enable) the work_items_rolledup_dates , work_item_epics_rollout and epic_and_work_item_associations_unification feature flag.

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Why were we not able to do this already? We wanted to have the ability to rollout epic work items to sub-groups.

What would happen if we don't do this? With a percentage based actor rollout, we would get an inconsistent experience within root groups