Adding an ability to configure max jitter

[rabbbit]

Hello!

Happy to provide PR for this, raising an issue first to see whether it would be considered.

Due to the internals of our metrics system, it would be highly beneficial for us to store samples at approximately (+/-1) the same frequency:

• [9s-11s],
• [19-21s],
• [29-31s],
• ...

This is currently not possible, as jitter is always double the scraping window - if we set the frequency to 10s, it'll scrape at random between and 20s.

Would you be open to adding a new flag housekeeping_max_jitter, as time.Duration so that we set:

housekeeping_interval = 9s
housekeeping_max_jitter = 2s

So that we get the desired behaviour?

An alternative would be to allow jitter to reduce the frequency of scraping, so we'd get the same behaviour with

housekeeping_interval= 10s
housekeeping_max_jitter = 1s
housekeeping_allow_negative_jitter = true

this seems like a more intuitive approach, but also a bit of a larger change. Happy to do either.