fix(Dockerfile): use busybox to set permissions

the docker tools do not behave as expected

Dockerfile

@@ -30,10 +30,10 @@ COPY shard.lock .
 
 RUN shards install --production --ignore-crystal-version --skip-postinstall --skip-executables
 
-# Add src (0777 as container may be launch as a random user)
+# Add src
 COPY ./src /app/src
-RUN mkdir -p /app/www && chmod 0777 /app/www
-RUN mkdir -p /app/tmp && chmod 0777 /app/tmp
+RUN mkdir -p /app/www
+RUN mkdir -p /app/tmp
 
 # Build application
 RUN PLACE_COMMIT=$PLACE_COMMIT \
@@ -77,8 +77,15 @@ COPY --from=build /usr/libexec/git-core/ /usr/libexec/git-core/
 # Copy the app into place
 COPY --from=build /app/deps /
 COPY --from=build /app/bin /
-COPY --from=build --chown=appuser:appuser --chmod=0777 /app/www/ /app/www/
-COPY --from=build --chown=appuser:appuser --chmod=0777 /app/tmp /tmp/
+
+COPY --from=build --chown=0:0 /app/www /app/www
+COPY --from=build --chown=0:0 /app/tmp /tmp
+
+# This seems to be the only way to set permissions properly
+COPY --from=build /bin /bin
+RUN chmod -R a+rwX /tmp
+RUN chmod -R a+rwX /app/www
+RUN rm -rf /bin
 
 # Use an unprivileged user.
 USER appuser:appuser