Add readonly settings to object service

[LeftofZen]

When updating the database schema, accounting for objects that are modified/uploaded during the time that schema/data upgrades are happening can be a pain. It is possible, but its a hassle. A much easier and safer method is to simply take the database offline so no changes can happen, but this means downstream uses like websites also go down. The middle ground is fortunately also simple - add a readonly mode to the service so that everyone can still use it, but no data changes so I don't need to worry about synchronising everything