Add app cron_timezone option to change the timezone used in cron_restart

[mgiova]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	#5618
License	MIT
Doc PR

Sometimes you need to restart a process on a time based on a different time-zone than the one used by the server and DST differences could cause problems. This PR adds an option to specify that time-zone that is passed as-is to the underlying Croner lib.

[CLAassistant]

All committers have signed the CLA.

[gkourpa]

This is a very basic feature and should definitely be added.