Implement throttle feature for the latte

[vponomaryov]

For the moment latte cannot limit maximum operations per second rate.
If a DB cluster, for any reason, temporary cannot serve the request rate generated by latte
then latte applies burst approach to compensate non-served requests.
It will make op/s be bigger than the configured rate.

So, need to implement the throttle mechanism to be able to limit the op/s for all the cases.
It is needed in the performance measuring scenarios.

[fruch]

so after looking it up in c-s, the outcome is that c-s behaves exactly the same in both options
but the calculation done with the HDR histogram is calculating service time = request time + wait time

so we leave that for the doing the calculation from HDR histogram as c-s, and not touch the implementation of how request are serves