Allow probes to configure their own interval

[guss77]

When running as a daemon, cloudscopes resamples the configured probes every settings: interval. Some probes - possibly application specific probes - may require a faster (or slower) sample rate.

To facilitate that a probe configuration may specify an interval parameter, that will specify the number of seconds (can be a fraction) between sampling. Interval timing will start immediately after the initial sampling session done when the daemon starts.