Cannot build tileserver on ARM64

[davenquinn]

This seems to be related to the lack of wheels for RasterIO for the ARM64 platform

• Support for pre-built aarch64/arm64 wheels rasterio/rasterio-wheels#69
• Add build support for arm64 developmentseed/titiler#740

[davenquinn]

This has now been resolved, but GDAL has to be separately installed in the container, which is probably better anyway. We fix this in #149 .