Move test information outside of `postprocessing`

[oscgonfer]

postprocessing has been used for two purposes lately, which are creating unnecessary bloat:

• processing of devices themselves (original purpose)
• store destination information when it's tested on the lab, before deliveries

The destination information is stored in the meta field in postprocessing. It was done that way to avoid changing things, but it got out of hand. The good thing is that we were fairly consistent and all test devices are marked as such in the system_tags (see example below), and the meta field is used

https://api.smartcitizen.me/devices/17659

I suggest making a new field for strings on devices, that simply store test-related information. This field would be then used to filter out test devices (which would also have the system-tag). When deploying, I suggest to clear postprocessing of all test devices, taking the meta information beforehand and placing it into the new field. This way, postprocessing is clean and we can keep ransaking it for the presence of non-nulls to search for devices.