Multiple Issue templates

Description including problem, use cases, benefits, and/or goals

To encourage users from following a standard, issue templates are extremely convenient.

Right now, you can have a single template, but this doesn't suffice in our experience.

Support for multiple issue templates.

Theses templates would be available as dropdown when creating or editing (in which case it should append the content) an issue.

the templates should be defined in the repository. I propose a directory structure such as:

alternatively:

Where we'd name the template after its filename.