feat: add per-recipe shell script support (#38)

Containerfile

@@ -8,6 +8,11 @@ ARG RECIPE
 COPY etc /etc
 # COPY usr /usr
 
+# copy scripts
+RUN mkdir /tmp/scripts
+COPY scripts /tmp/scripts
+RUN find /tmp/scripts -type f -exec chmod +x {} \;
+
 COPY ${RECIPE} /tmp/ublue-recipe.yml
 
 # yq used in build.sh and the setup-flatpaks recipe to read the recipe.yml