Add a weekly dump of the Garmin database

garmin-dump.timer runs garmin-dump weekly, keeping the two newest ISO weeks in
~/.local/share/negsplit/dumps, which simple_backup then copies; the login comes
from ~/.config/negsplit/dump.cnf (not tracked).

.config/systemd/user/garmin-dump.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=Dump the Garmin database to ~/.local/share/negsplit/dumps
+StartLimitIntervalSec=2h
+StartLimitBurst=4
+
+[Service]
+Type=oneshot
+ExecStart=%h/.local/bin/garmin-dump
+# MariaDB not up yet (e.g. caught up right after boot)? retry a few times
+Restart=on-failure
+RestartSec=5min

.config/systemd/user/garmin-dump.timer

@@ -0,0 +1,9 @@
+[Unit]
+Description=Dump the Garmin database weekly
+
+[Timer]
+OnCalendar=weekly
+Persistent=true
+
+[Install]
+WantedBy=timers.target