Ability to pause backups and repairs during restore

[pdbossman]

While performing a restore of a keyspace into a cluster that already existed and was live for other applications, the regularly scheduled backups and repairs started and interfered with the restore.

It would be nice to have an option added to sctool suspend
--exclude-restore

[pdbossman]

In the absence of this capability, procedurally I do the following:

• perform a repair of existng cluster objects
• perform a backup of existing cluster objects
• for each backup and repair:
  sctool repair update -c CLUSTER-ID SCHEDULED-REPAIR-TASK-ID --enabled=false
  sctool backup update -c CLUSTER-ID SCHEDULED-REPAIR-TASK-ID --enabled=false
• ... then start restore...
• after the restore completes, re-enable scheduled backup/repairs

[karol-kokoszka]

The description of the task is quite clear.
Right now, we have only the possibility of suspending the whole cluster what means that no tasks will be executed (including restore) -> https://manager.docs.scylladb.com/stable/sctool/suspend-resume.html .

Let's just mark is as "ready-for-development" and include into the next milestone (after 3.4).

[Michal-Leszczynski]

Ref #3742.