kdump-steamos: Move configuration file out of /etc

This patch main goal is to "un-Debianize" the configuration file
for kdump-steamos - thanks Emil (@xexaxo) for the discussions; it
is with a bit of a heavy heart I do that, but let's comply with the
modern distros ;-)

We hereby put the config file in a more standard path: /usr/share.
Usually users could override that with /etc/ file, but not in this
case, or at least, not for now. Kdump/pstore is expected to work
quietly, with no users' interference. Advanced users might want to
play with the configs though; and those can just go ahead and edit
the /usr/share/kdump/kdump.conf - it's all documented in the README.

In the future we can improve that by having the override mechanism
with the /etc file, let's see if we have a demand for that.

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

kdump.conf

@@ -0,0 +1,45 @@
+#!/bin/sh
+#
+#  SPDX-License-Identifier: LGPL-2.1+
+#
+#  Copyright (c) 2021 Valve
+#
+#  Configuration settings for SteamOS kdump. After _any_ change in this
+#  file, it's required to create the kdump minimal initramfs by running:
+#  /usr/lib/kdump/kdump-load.sh initrd
+#
+
+#  Mount-related options - the DEVNODE points to the /home directory link;
+#  this is used to derive the numerical devnode for kdump, since the link
+#  is not present so early in the system boot. The KDUMP_FOLDER will be
+#  created if doesn't exist. The KDUMP_MNT is just a temporary file that
+#  carries the mounted folder path across boot-time scripts.
+
+MOUNT_DEVNODE="/dev/disk/by-partsets/shared/home"
+KDUMP_FOLDER="/.steamos/offload/var/kdump"
+KDUMP_MNT="/tmp/kdump.mnt"
+
+#  Kdump controlling settings - for now we don't have network/iscsi dumps, only
+#  local storage dumps. If FULL_COREDUMP is !=0, we collect a full compressed
+#  vmcore, which might require a lot of disk space. The *_CMD settings refer
+#  to tunings on makedumpfile - we rely on zstd compression and maximum page
+#  exclusion for the full vmcore, mimic'ing Debian kdump. Finally, GRUB_AUTOSET
+#  determines if kdump-steamos should try to automatically set grub.cfg in
+#  order to reserve memory for kdump (if needed, i.e., when pstore is not in
+#  use) - keep it as '1' for enabling the mechanism (this is the default).
+
+FULL_COREDUMP=0
+MAKEDUMPFILE_COREDUMP_CMD="-z -d 31"
+MAKEDUMPFILE_DMESG_CMD="--dump-dmesg"
+GRUB_AUTOSET=1
+
+#  Pstore-RAM setting - if enabled, Kdump won't be loaded, instead the Pstore
+#  RAM backend will be configured. In order to have success, this operation
+#  relies in having an available RAM buffer on /proc/iomem with at least 5MiB
+#  in size.
+USE_PSTORE_RAM=1
+
+#  By default, collected logs are submitted automatically to Valve servers.
+#  Setting LOG_SUBMISSION to '0' will disable this behavior; but notice that
+#  even with the log submission disabled, the logs are saved locally.
+LOG_SUBMISSION=1