Handling variables in the watched URL

@todo update

Sometimes you need to insert the current date, this can be done following the Jinja2 template syntax, you can also use any other Jinja2 syntax (for example, if the day is a tuesday, then insert the word "foobar" or something)

https://changedetection.io/test.txt?date={% now 'Europe/Berlin', '%d' %}.{% now 'Europe/Berlin', '%m' %}.{% now 'Europe/Berlin', '%Y' %}

Would request (according to the Europe/Berlin) timezone

https://changedetection.io/test.txt?date=24.10.2022

List of accepted timezones https://en.wikipedia.org/wiki/List_of_tz_database_time_zones

List of date format codes (the %d etc) https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes