Deb: Add manually dh_systemd_start snippets

These do now show up automatically due to init and systemd customizations,
so the handiest fix is to add them manually. This has been the praxis
in downstream MariaDB packaging for a couple years now, and works fine.

- Ensure service is loaded and started after installation,
  (fixes service start issues in Debian/Ubuntu upgrades where
  otherwise service mysql status stayed stopped)

- Ensure service stopped before removal/purge
  (fixes unstopped processes detected by piuparts)

- Ensure systemd daemon is reloaded after removal/purge when service
  has been removed

debian/mariadb-server-10.5.postinst

@@ -235,3 +235,14 @@ if [ -x "$(command -v deb-systemd-helper)" ]; then
 fi
 
 #DEBHELPER#
+
+# Modified dh_systemd_start snippet that's not added automatically
+if [ -d /run/systemd/system ]; then
+	systemctl --system daemon-reload >/dev/null || true
+	deb-systemd-invoke start mariadb.service >/dev/null || true
+# Modified dh_installinit snippet to only run with sysvinit
+elif [ -x "/etc/init.d/mariadb" ]; then
+	if [ "$1" = "configure" ] || [ "$1" = "abort-upgrade" ]; then
+		invoke-rc.d mariadb start || exit $?
+	fi
+fi

debian/mariadb-server-10.5.postrm

@@ -89,3 +89,8 @@ if [ "$1" = "purge" ] && [ -f "/var/lib/mysql/debian-$MAJOR_VER.flag" ]; then
 fi
 
 #DEBHELPER#
+
+# Modified dh_systemd_start snippet that's not added automatically
+if [ -d /run/systemd/system ]; then
+	systemctl --system daemon-reload >/dev/null || true
+fi

debian/mariadb-server-10.5.prerm

@@ -2,3 +2,11 @@
 set -e
 
 #DEBHELPER#
+
+# Modified dh_systemd_start snippet that's not added automatically
+if [ -d /run/systemd/system ]; then
+	deb-systemd-invoke stop mariadb.service >/dev/null
+# Modified dh_installinit snippet to only run with sysvinit
+elif [ -x "/etc/init.d/mariadb" ]; then
+	invoke-rc.d mariadb stop || exit $?
+fi