Warn when addr:*=* is added to a relation

[gy-mate]

This is an issue moved from openstreetmap/iD#10642.

addr:*=* tags are not allowed on relations (except multipolygon relations):

• https://wiki.openstreetmap.org/wiki/Key:addr:*#:~:text=Used%20on%20these%20elements
• https://wiki.openstreetmap.org/wiki/Talk:Key:addr:*#on_relations

Therefore, I think that Osmose should warn users when this "rule" isn't met.

[Famlam]

I think this can easily be done with mapcss.
Sorry for proposing another forward, but it may be better to report this to JOSM. If they add it to their rules, it'll automatically be synchronized into Osmose, so then you have detection at the source and in a QA tool. What do you think?