switch to rasterio 1.2.4

[vincentsarago]

The new rasterio wheels are now shipped with GDAL 3.3 (🥳 thanks @sgillies). As mentioned in previous issues, GDAL >2,4;<3.3 suffered of performances issues due to the new PROJ 8 (sqlite database). Thanks to Even Rouault (OSGeo/gdal#3591) the new GDAL 3.3 fix most of the performance downgrade we were seeing.

There is still a difference but IMO it's acceptable (because GDAL3 also provide new improvement).

Thus I propose we remove the hardcoded rasterio pin in the official TiTiler image https://github.com/developmentseed/titiler/blob/master/Dockerfile#L8-L10

ref: cogeotiff/rio-tiler#346 (comment)

[vincentsarago]

Done in #327