Add tablet task manager module and keep it in storage_service.
Introduce tablet_virtual_task that covers tablet repair.
Thanks to a repair virtual task, a user can check the list of pending
repairs, get the status of a specific repair, or abort it using the task
manager API.
Fixes: #21368.
No backport, new feature
Closesscylladb/scylladb#21624
* github.com:scylladb/scylladb:
test: add test to check tablet repair tasks
test: topology_tasks: enable tablets
service: keep tablets module in storage_service
service: rename storage_service::_task_manager_module
service: add tablet_virtual_task
tasks: utilize preliminary virtual task lookup
b87fb94a5e