Add issue templates

[lengau]

We should have GitHub issue templates following the new templates. However, this differs for applications and libraries, so we'd need to consider how to do so as well.

• Library example: github: add issue templates craft-application#37
• Application example: github: add issue templates charmcraft#1106

Marking this as help wanted because I don't immediately have a good way to do it. Notably the bug template is quite different. I'd love to hear ideas from anyone who might have them, as currently the best I have is to use the library template for now (which would be an appropriate template for starbase itself) and include the application template elsewhere with documentation about updating it if we want to use it.