awstats.schoolserver.conf.j2: Set AllowFullYearView=3 not 2

[holta]

This PR essentially fixes AWStats's full year view, by setting /etc/awstats/awstats.schoolserver.conf to a far more useful default.

Allowing folks to bypass this ugly error/warning when they select "- Year -" at the bottom of the dropdown where you pick a month:

Error: Full year view has not been allowed from a browser (AllowFullYearView should be set to 3).

Setup ('/etc/awstats/awstats.conf' file, web server or permissions) may be wrong.
Check config file, permissions and AWStats documentation (in 'docs' directory).

Tested on Raspberry Pi OS Lite on RPi 4.