New VRT pixel function - quantile

[h-a-graham]

Feature description

With GDAL version 3.12.0 we now have a host of new VRT pixel functions including, for example, the median. I've been implementing a quantile python pixel function which tends to be quite slow and was wondering if there would be interest in adding a native GDAL quantile/percentile pixel function to VRT?

Additional context

If considered appropriate, I would be happy to submit a pull request for this feature (as long as a novice c++ attempt at this doesn't take up too much of your time). Cheers!

[rouault]

if there would be interest in adding a native GDAL quantile/percentile pixel function to VRT?

sure