Support OpenPGP WKD

We should add support for the OpenPGP WKD protocol in AlekSIS (for mail domains hosted by an AlekSIS-App-Postbüro

https://tools.ietf.org/id/draft-koch-openpgp-webkey-service-07.html#rfc.section.3

moved from Teckids/ticdesk#76 (moved)

added part::backend workflow::new-app labels

changed the description