devctr: add zstd

Stage it so next time we rebuild the devctr it's there, and we can use
it to replace gzip, since it compresses better and faster.

Signed-off-by: Pablo Barbáchano <[email protected]>

Author: pb8o

tools/devctr/Dockerfile

@@ -75,7 +75,7 @@ RUN apt-get update \
         screen tmux \
         tzdata \
         tini \
-        squashfs-tools \
+        squashfs-tools zstd \
         # for aws-lc-rs
         cmake \
         # for Qemu vhost-user-blk backend