create issue templates for contributions

[lzehl]

e.g. for different instance contributions vs. vocabulary contributions vs. schema contributions vs. extensions (?)

@openMetadataInitiative/openminds-developers let's discuss how those template should look and where they should be provided.

[apdavison]

see https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests

[lzehl]

@Raphael-Gazzotti we should keep this in mind but this is low priority for me at the moment.