feat: Allow filenames in VERSION (#381)

Dockerfile

@@ -1,5 +1,5 @@
 FROM scratch
-COPY --from=qemux/qemu-docker:4.20 / /
+COPY --from=qemux/qemu-docker:4.21 / /
 
 ARG DEBCONF_NOWARNINGS "yes"
 ARG DEBIAN_FRONTEND "noninteractive"

src/install.sh

@@ -93,6 +93,7 @@ fi
 CUSTOM=$(find "$STORAGE" -maxdepth 1 -type f -iname custom.iso -printf "%f\n" | head -n 1)
 [ -z "$CUSTOM" ] && CUSTOM=$(find "$STORAGE" -maxdepth 1 -type f -iname boot.iso -printf "%f\n" | head -n 1)
 [ -z "$CUSTOM" ] && CUSTOM=$(find "$STORAGE" -maxdepth 1 -type f -iname custom.img -printf "%f\n" | head -n 1)
+[ -z "$CUSTOM" ] && CUSTOM=$(find "$STORAGE" -maxdepth 1 -type f -iname "${VERSION/\/storage\//}" -printf "%f\n" | head -n 1)
 
 ESD_URL=""
 MACHINE="q35"