add possibility to have no jitter with RandomFixedWindowSampler

[AlexandreAndr]

The objective is to have an in-between of SequentialFixedWindowSampler and RandomFixedWindowSampler . We want to have samples drawn randomly but without any jitter.
The functionality can be implemented in one of the two samplers.
After discussion with Vinam, the design choice was more oriented to RandomFixedWindowSampler .
If there are better design choices do not hesitate!
With this implementation, Jitter can be disabled by setting enable_jitter to False at RandomFixedWindowSampler initialization

[mazabou]

What is the use case for this? @vinamarora8 @AlexandreAndr

Technically this behavior can be achieved by changing the interval_dict to have intervals with the exact same length of the desired trial, that way there won't be any jitter.

[AlexandreAndr]

I think I get it.
Do you mean if we have window_length that has the same length as the intervals in interval_dict, doesn't it apply a jiter?