[MapProxy] Generate lower zoom level tiles from higher zoom level tiles

[Pablo Sanfilippo]

Hello. I have a WMS server that renders a map from multiple images. It
works fine at high zoom levels (where just a few images need to be merged)
but it has trouble rendering the map at a low zoom level because it has to
read a lot of images from disk. I know I can limit MapProxy to only query
at certain zoom level by using min_res/max_res. But if a query is made
outside that boundaries, MapProxy will return a blank image, right? Is
there a way for MapProxy to generate a lower zoom level tile by merging
together a set of higher zoom level tiles? Maybe in the seeding process?

Thanks!

Pablo