MSPT Jitter

[AuroraLS3]

I would like to be able to..

Measure how stable server ticks are.

Is your feature request related to a problem? Please describe.

Jitter is a measure how much a value changes over time.
This can be used to measure how stable the TPS computation is.

Example MSPT series:
35, 36, 34, 80, 37

Differences:
1, 2, 46, 43

Average jitter:
23

Because MSPT is computed every 50ms it doesn't make sense to calculate Jitter based on the already stored Average MSPT, since that one is stored once per 60000ms (1200 measurements)

It should be a new column on the plan_tps table.