Add GitHub issue templates for tasks, features and bugs as well

[oliverklee]

Goal

I as a user want to have different templates for different issues

Acceptance criteria

• we have agreed on the templates
• the templates are created and the user can select them
• the templates ask for acceptance criteria (or for bugs for the actual and expected behavior)

Additional Information

Currently, when you create an issue, we only have buttons for technical feedback and security vulnerabilities. We want to cover the other cases as well (particularly for in-team use, which usually would not fit in the "technical feedback" category).

[linxpinx]

i have added 3 layouts as a basis for discussion

[DanielSiepmann]

We decided to have the goals/acceptance criteria within the template for features/tasks.

[lukaszuznanski]

@oliverklee I guess that's done

[oliverklee]

@lukaszuznanski No, we still need a template for bug reports.