In most cases, tasks manager's tasks are started just after they are
created. Thus, to reduce boilerplate required for creating and starting
tasks, tasks::task_manager::module::make_and_start_task method is added.
Repair tasks are modified to use the method where possible.
Closes#12729
* github.com:scylladb/scylladb:
repair: use tasks::task_manager::module::make_and_start_task for repair tasks
tasks: add task_manager::module::make_and_start_task method