Build wgrib2 with PNG + AEC decoders

Prod wgrib2 3.6.0 was built without PNG support (cmake had no
-DUSE_PNG flag) so MrmsFetchWorker crashed on every tick with
'packing type 41 not supported' — MRMS PrecipRate tiles are
PNG-compressed (GRIB2 DRT 5.41). libpng-dev was already in the
builder stage; the cmake invocation just never asked wgrib2 to
use it.

Also turn on -DUSE_AEC=ON since libaec-dev is already installed
and some HRRR native-grid variables ship with AEC/CCSDS 121
compression.

Dockerfile

@@ -37,6 +37,7 @@ RUN wget -q --content-disposition "https://github.com/NOAA-EMC/wgrib2/archive/re
   && cd wgrib2-${WGRIB2_VERSION} \
   && mkdir build && cd build \
   && cmake .. -DCMAKE_INSTALL_PREFIX=/usr/local -DCMAKE_BUILD_TYPE=Release \
+       -DUSE_PNG=ON -DUSE_AEC=ON \
   && make -j$(nproc) \
   && make install \
   && strip /usr/local/bin/wgrib2