Adding Generic Dask-Image Filter to Clean Subpackage and Potential Rename of Subpackage

[ctuguinay]

From discussion w/ Wu-Jung on #1326:

Having a wrapper around Dask-Image's generic_filter would be a pretty good thing to have in Echopype, and it will already be used in the binning implementation of echopype.clean.mask_transient_noise. Having it with all the other image masking functions (noise and attenuation masking) would not fit the Clean subpackage name, since the filter being applied doesn't necessarily need to be used for 'cleaning', since it can be used to extract temporal-spatial information about the echogram. One possible rename option would be Filter, but there are other filtering operations that occur in echosounder data processing that isn't necessarily on the Echogram level. One such example is the match filtering that happens in calibrating Sv.