Tutorial Tailscale update notifications and automatic updates 2024.08.04

The automatic update email used to always include a suggestion to do a manual installation. This made no sense if the update had already been installed. Now the manual installation message only appears in the automatic update email if we are performing a dry run.

A dry run goes through the motions but installs nothing at all.

Thanks to @lp_ge we now have a zero-configuration version. The scripts now read the synology config file and no longer need manual editing of the email address for notifications to work.

Workaround for tailscale issue 12203 which causes the outbound connection configuration to be lost. The ts_update.sh script will run tailscale's outbound connection configuration script if it notices that the outbound connection configuration was lost during the update.
Also the ts_update.sh script will skip the email notification if mail_to is not set instead of generating an error.

When converting the days_to_wait variable to minutes we subtract one minute otherwise when scheduling the task to run daily it may end up waiting an extra day. The find command has no greater than or equal ("+n for greater than n").