monitoring: relax cpu provisioning alert with longer duration

Created by: bobheadxi

Brief peaks for CPU usage are not particularly useful indicators that a service might be underprovisioned - it might even be desired behaviour, we want services to occasionally be capable of using up almost all of its capacity when needed. If a service consistently experiences high CPU usage peaks, however, that's a stronger sign that a service might require more resources.

Discussed with @slimsag briefly earlier in the week about this, since it is a very frequently firing alert.