feat(restore): adds exclusive cluster lock for restore task

[VAveryanov8]

This makes the scheduler run the restore task only if no other tasks (backup or repair) are running in the cluster. Conversely, other tasks (backup or repair) won't start if the restore task is running in the cluster at that time.

Fixes: #4045.

---

Please make sure that:

• Code is split to commits that address a single change
• Commit messages are informative
• Commit titles have module prefix
• Commit titles have issue nr. suffix

[VAveryanov8]

This is how output of a ./sctool task looks like, when either backup/repair task can't start due to exclusive lock:

╭──────────────────────────────────────────────┬────────┬──────────────┬────────┬──────────────────┬─────────┬───────┬────────────────────────┬────────────────────────┬─────────────┬────────────────────────╮
│ Task                                         │ Labels │ Schedule     │ Window │ Timezone         │ Success │ Error │ Last Success           │ Last Error             │ Status      │ Next                   │
├──────────────────────────────────────────────┼────────┼──────────────┼────────┼──────────────────┼─────────┼───────┼────────────────────────┼────────────────────────┼─────────────┼────────────────────────┤
│ backup/06cd5d90-6daa-4215-acd3-d19f6782b5b6  │        │              │        │ Europe/Warsaw    │ 0       │ 1     │                        │ 25 Nov 24 09:13:52 CET │ ERROR (0/3) │ 25 Nov 24 09:23:52 CET │
│ restore/f514523c-5015-486f-b25f-22e59c5b5962 │        │              │        │ Europe/Warsaw    │ 0       │ 0     │                        │                        │ RUNNING     │                        │
╰──────────────────────────────────────────────┴────────┴──────────────┴────────┴──────────────────┴─────────┴───────┴────────────────────────┴────────────────────────┴─────────────┴────────────────────────╯

and this is how output of a ./sctool progress ... looks like:

$  ./sctool.dev progress -c my-cluster backup/06cd5d90-6daa-4215-acd3-d19f6782b5b6
Run:            351378ee-ab05-11ef-aa2d-0242c0a8c802
Status:         ERROR (initialising)
Cause:          exclusive task (restore) is running: another task is running
Start time:     25 Nov 24 09:13:52 CET
End time:       25 Nov 24 09:13:52 CET
Duration:       0s
Progress:       -

[Michal-Leszczynski]

Really nice tests!
Just left a small refactor oriented comments.

[Michal-Leszczynski]

This is how output of a ./sctool task looks like, when either backup/repair task can't start due to exclusive lock:

The strange thing is that we report it as an error, but that's not connected to this PR at all.
On the other hand, it encourages user to look at the sctool progress output, so that's a good thing.
Anyway, the sctool progress error message looks good!

[Michal-Leszczynski]

Refs: 4045.

Why not Fixes?

[VAveryanov8]

@Michal-Leszczynski I've updated the pr, I'd appreciate if you could take a look one more time.

[Michal-Leszczynski]

Nice job!