all: Move the multi-configuration file reading routine to a common helper

Based on Emil's (xexaxo) feedback, we now have a common.sh file
that contains the implementation of the routine to read all config
files for kdump/pstore, and we use Makefile to join the files,
having the same implemention in all users.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

save-dumps.header

@@ -0,0 +1,11 @@
+#!/bin/bash
+set -uo pipefail
+#
+#  SPDX-License-Identifier: LGPL-2.1+
+#
+#  Copyright (c) 2021 Valve.
+#  Maintainer: Guilherme G. Piccoli <gpiccoli@igalia.com>
+#
+#  This is the kdump/pstore log collector; this script prepares the
+#  collected data and save it in the local disk, in the next successful boot.
+#