Feature request: time-based rolling window functionality

Hi,

I was hoping you would consider extending the rolling window functionality to time windows; as far as I can tell any rolling window functions simply work across a number of nearby points, and not points within, (say) an hour or minute window. This means that I can't even find a reliable rolling mean without writing code myself (and as I am relatively new to Python, this inevitably ends up uselessly slow)

This would extend all rolling functionality to unevenly sampled data, and to buggy data with quality gaps. It would also allow me/others to fix such datagaps by averaging and downsampling where appropriate.

(Context: basically all space physics data and probably other fields too. Really, this would need to be a centred window - I think pandas has a non-centred time window but that doesn't help much.)

Thanks for reading this! And sorry if this is already available - I couldn't find any settings for it.

(PS the multidimensionality of xarray is so useful for me, I have so many vector observations in so many different co-ordinate systems!)

Review xarray's existing rolling-window functionality and compare it with pandas' time-based windows, focusing on the request for centered windows over unevenly sampled data. Done would mean defining and implementing the proposed time-based rolling behavior across the rolling functionality, with coverage for gaps and multidimensional data.