Fixed orphaned dashboards (#9590)

Delete empty dashboards without an owner
Chown dashboards that have widgets to the first admin level user

fixes: #9580 

DO NOT DELETE THIS TEXT

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sql-schema/276.sql

@@ -0,0 +1,2 @@
+DELETE FROM dashboards WHERE user_id NOT IN (SELECT user_id FROM users) AND dashboard_id NOT IN (SELECT DISTINCT dashboard_id FROM users_widgets);
+UPDATE dashboards SET user_id = (SELECT user_id FROM users WHERE level = 10 LIMIT 1) WHERE user_id NOT IN (SELECT user_id FROM users);