Add native Debian Packaging for Linux

Currently, the Debian packages are generated from ALIEN that converts
RPMs to Debian packages. This commit adds native Debian packaging for
Debian based systems.

This packaging is a fork of Debian zfs-linux 2.1.6-2 release.
(source: https://salsa.debian.org/zfsonlinux-team/zfs)

Some updates have been made to keep the footprint minimal that
include removing the tests, translation files, patches directory etc.
All credits go to Debian ZFS on Linux Packaging Team.

For copyright information, please refer to contrib/debian/copyright.

scripts/debian-packaging.sh can be used to invoke the build.

Reviewed-by: Mo Zhou <cdluminate@gmail.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Umer Saleem <usaleem@ixsystems.com>
Closes #13451

contrib/debian/tree/zfs-initramfs/usr/share/initramfs-tools/conf.d/zfs

@@ -0,0 +1,8 @@
+for x in $(cat /proc/cmdline)
+do
+	case $x in
+		root=ZFS=*)
+			BOOT=zfs
+			;;
+	esac
+done

contrib/debian/tree/zfs-initramfs/usr/share/initramfs-tools/hooks/zdev

@@ -0,0 +1,67 @@
+#!/bin/sh
+#
+# Add udev rules for ZoL to the initrd.
+#
+
+PREREQ="udev"
+PREREQ_UDEV_RULES="60-zvol.rules 69-vdev.rules"
+COPY_EXEC_LIST="/lib/udev/zvol_id /lib/udev/vdev_id"
+
+# Generic result code.
+RC=0
+
+case $1 in
+prereqs)
+	echo "$PREREQ"
+	exit 0
+	;;
+esac
+
+for ii in $COPY_EXEC_LIST
+do
+	if [ ! -x "$ii" ]
+	then
+		echo "Error: $ii is not executable."
+		RC=2
+	fi
+done
+
+if [ "$RC" -ne 0 ]
+then
+	exit "$RC"
+fi
+
+. /usr/share/initramfs-tools/hook-functions
+
+mkdir -p "$DESTDIR/lib/udev/rules.d/"
+for ii in $PREREQ_UDEV_RULES
+do
+	if [ -e "/etc/udev/rules.d/$ii" ]
+	then
+		cp -p "/etc/udev/rules.d/$ii" "$DESTDIR/lib/udev/rules.d/"
+	elif [ -e "/lib/udev/rules.d/$ii" ]
+	then
+		cp -p "/lib/udev/rules.d/$ii" "$DESTDIR/lib/udev/rules.d/"
+	else
+		echo "Error: Missing udev rule: $ii"
+		echo "       This file must be in the /etc/udev/rules.d or /lib/udev/rules.d directory."
+		exit 1
+	fi
+done
+
+for ii in $COPY_EXEC_LIST
+do
+	copy_exec "$ii"
+done
+
+if [ -f '/etc/default/zfs' -a -r '/etc/default/zfs' ]
+then
+	mkdir -p "$DESTDIR/etc/default"
+	cp -a '/etc/default/zfs' "$DESTDIR/etc/default/"
+fi
+
+if [ -d '/etc/zfs' -a -r '/etc/zfs' ]
+then
+	mkdir -p "$DESTDIR/etc"
+	cp -a '/etc/zfs' "$DESTDIR/etc/"
+fi