Refactor rolled up dates service to use callbacks
What does this MR do and why?
Move the work item rolled up dates widget service to the new callback classes architecture.
Related to #412801 (closed)
More info in https://docs.gitlab.com/ee/development/work_items_widgets.html#widget-callbacks
MR acceptance checklist
Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
How to set up and validate locally
Tests in ee/spec/requests/api/graphql/mutations/work_items/update_spec.rb
validate that the update mutation still works as before.
Edited by Heinrich Lee Yu