Return an error if downtime db connection fails while creating or del…

[jnation3406]

…eting realtime session. Also create a configuration status for realtime observations

There's two things being fixed in this PR.

1. If the downtime DB connection fails when trying to create or delete a realtime session, it used to still create/delete the corresponding observation in the obs portal. Now it should kick back an error to the caller saying to try again, since the downtime db connection stuff is usually transitory.
2. The realtime observations didn't have configuration statuses created, since they have no configurations. But configuration statuses are necessary for the site software to report back status on the observation. The migration is just to allow null for configuration on a configuration status. I didn't want to create a useless configuration + all the stuff it needs (constraints, target, etc.) for a realtime observation since its not necessary.