fix scheduler scheduling & preempting attempt metrics

[lzlaa]

In the current implementation, when the Scheduling and Preempting stages fail, both scheduler_pod_scheduling_attempts{unschedulable} and scheduler_pod_preempting_attempts{nominatedFailure} will be recorded, leading to unclear semantics for these metrics.

In this MR:

• when Scheduling and Preempting both fail: scheduler_pod_scheduling_attempts{unschedulable} += 1; scheduler_pod_preempting_attempts{nominatedFailure} += 1
• when Scheduling fails but Preempting succeeds: scheduler_pod_scheduling_attempts{scheduled} += 1; scheduler_pod_preempting_attempts{nominated} += 1

[zryfish]

@lzlaa Please rebase and push again

[NickrenREN]

any new comments on this PR ? @zryfish @binacs

[binacs]

lgtm