Expose gaps in moving window

[daniel-zullo-frequenz]

What's needed?

Implement method to return the maximum data gap in a MovingWindow given timestamp or index ranges representing a window size

Proposed solution

Compute the maximum data gap size iterating through the MovingWindow data gaps (underlying buffer) for the given timestamp or index ranges representing a window size

Use cases

Actors like peak-shaving needs this functionality to avoid implementing it on their ends.

Update

Note the scope of the issue was updated as follows:
The MovingWindow will provide access to a list of all gaps in a defined subset of the moving window. Applications can get the maximum gap or the sum of gaps by using something like max(g.duration for g in gaps) or sum(...), respectively.

[daniel-zullo-frequenz]

fyi @matthias-wende-frequenz @idlir-shkurti-frequenz

Please feel free to amend/correct the issue description accordingly