Provide auto-update mechanism for templates

[Blesmol]

Support an auto-update mechanism for the template file(s) so that changes and improvements to the chronicle templates or scenario-specific settings automatically reach the users.

For this, the program would try to reach a well-defined URL (e.g. here on github) that holds information on the latest templates. In case the local program finds newer information, it could automatically download the new templates and store on the local machine. This should be made transparent to users and configurable so that users can switch this off. Or only be triggered by a special command, e.g. pfsct template update or the like.

The program itself won't get an auto-update mechanism now. Maybe using the same mechanism it could check the centrally available version and output a notification if a new version is available.

[Blesmol]

Separate repository (pfsct-templates?), github action that creates new overview file on push to master branch