Automatically create issue for new exercise or key feature icons

[ErikSchierboom]

configlet will be hardcoding the allowed icons for exercises and key features. To ensure that configlet remains up to date, we should add a CI workflow that detects if a new icon was added and create an issue in the configlet repo accordingly (or even a PR!).

[iHiD]

OK, cool. Nice idea. FYI, currently the key-features icons live in the website but we should change that.