* limit number of characters for ntfy.sh to 4000
* make sure we send ntfy.sh notification only once

Add stamps for ntfy as well to make sure that the message is sent just
once. Up to now when ntfy was enabled and e-mails disabled, message
queue was processed every five minutes and notifications were sent all
over again till they were dismissed or mailed.

ntfy has a limit of 4000 characters per message, otherwise massage is
handled as an attachment and treated differently. This way we make sure
our notifications fit within the limit.

Adding ntfy support

Michal Hrusecky authored Dec 20, 2022 and Josef Schlehofer committed Dec 20, 2022

ntfy [1] is the free and open-source service that can push notifications to your phone or desktop.
By default, I decided to use high priority [2] which allows to have pop-over
notification with a default notification sound.

[1] https://ntfy.sh/
[2] https://docs.ntfy.sh/publish/#message-priority

Andrew Latham authored Jul 23, 2022 and Martin Matějek committed Jul 26, 2022

Now we get the exact restart time including the timezone.

It fixes the ambiguity of scheduled restart time, in case there are
multiple Turris devices located within different timezones.

Closes: #11



[Add timezone to cs timestamp as well.]
Co-authored-by: Martin Matějek <martin.matejek@nic.cz>

And simplify `install` target

- Avoid unreadable spaghetti code
- Avoid to access inexistent message files
    - Which leads to failed command
    - And generates useless error messages
- Generate warning when no message text is found

Also drop evaluation of escape characters in the file

Cycle through files properly, simplify cycle variable and avoid
evaluation of subshell stdout

- The value of `compat` variable was in fact negated
- New (and preffered) way to call the script was not included in usage
- Also generate a warning when running in compatible mode

Rely on PATH env variable

- Compare string rather than execute variables content (which is
  potentially insecure)
- Do not evaluate variables in arithmetic environment

Even though notification with empty message is not the expected kind of
notification and it make no sense to create such notification,
list_notification should export expected json structure and fallback to
empty string in its output.

`exit` is trapped to call unlock anyway

- mail_from is needed in compose_message and create_msmtp_config
- defined turris_smtp comes handy