TPA-RFC-19: review labels vs projects usage

after today's all hands, I (re-)realized that we have some issues with the way we organize tickets around here. some services have their own project (e.g. tpo/tpa/gitlab) while some only have a label here (e.g. Nextcloud). and then some services don't have a label at all! (e.g. there's no Ganeti label!).

this should really be fixed. we should:

• clarify when it's appropriate to have a project vs a label for a service
• add labels (or projects?) for any service that's missing one?
• update the service template to make sure this decision is made when documenting the service
• add a description for all labels
• ~~decide what to do about the Schleuder and Gitlab labels (either move those issues to their respective projects and drop the label, or drop the projects)~~ both will be kept.

might be worth further discussion (RFC?)