Favorite lists (#654)

Add tests

Remove the favorites pseudo namespace if there are no lists or tasks favorited

Regenerate swagger docs

Fix favorite lists not being updated because of nonexisting users (the favorite list does not have one)

Make the pseudo favorites list always favorited

Add favorited lists to the favorites pseudo namespace

Add favorite field to list

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/654

pkg/swagger/docs.go

@@ -6545,6 +6545,10 @@ var doc = `{
                     "description": "Whether or not a list is archived.",
                     "type": "boolean"
                 },
+                "is_favorite": {
+                    "description": "True if a list is a favorite. Favorite lists show up in a separate namespace.",
+                    "type": "boolean"
+                },
                 "namespace_id": {
                     "type": "integer"
                 },