add: file to prune dockerfiles

Use this file to prune Dockerfiles before getting their hash.

- remove empty lines, comments, and timestamp

Author: jakubk

docker/prune_dockerfile.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+if [ -z "$1" ]; then
+  echo "Usage: $(basename $0) <input_filepath>"
+  exit 1
+fi
+
+# Remove empty lines, comments, and timestamp.
+sed -e '/\s*#.*$/d' -e '/^\s*$/d' -e '/generation_timestamp/d' "$1"