Create templates for Issues in all Spyderisk projects

[danshearer]

The file CONTRIBUTING.md in Spyderisk GitHub projects (for example, this one for system-modeller gives links for creating new issues.

@kenmeacham pointed out that CONTRIBUTING.md doesn't advise users to look for their problem in existing issues first, before potentially wasting time asking for help. It also tells users to select a template, but none exist yet. I propose that we create these templates for the main projects, and that we have careful wording that covers Ken's point and other things, rather than trying to cover them in CONTRIBUTING.md, which is more general.