feat: add fitError when no available clusters

[Poor12]

When there is no available clusters, scheduler will result in a FitError, and we can get the scheduling details from events.

 Warning  ScheduleFederatedObject  17m (x4 over 17m)     scheduler                  0/3 clusters are available: 1 cluster(s) didn't match cluster selector, 2 cluster(s) were not in placement list

[gary-lgy]

Looks like our webhook plugins do not return a reason when a cluster is unschedulable. Should we open an issue to track it?

[Poor12]

Looks like our webhook plugins do not return a reason when a cluster is unschedulable. Should we open an issue to track it?

Sure, maybe we can propose one right now, such as ("cluster(s) were filtered by webhookPlugin(%s)", p.name)

[gary-lgy]

Looks like our webhook plugins do not return a reason when a cluster is unschedulable. Should we open an issue to track it?

Sure, maybe we can propose one right now, such as ("cluster(s) were filtered by webhookPlugin(%s)", p.name)

I was thinking more along the lines of letting webhooks return their own reasons. This would require extending our request and response definitions. For now, I think we can adopt your suggestion.