Namespaced userdata

[pinkwah]

In order to make userdata more useful, we could make the JSON be namespaced based on what project uses it. Eg, webviz-ert and ert could be namespaces under which they put data. For example, ert can have name under it, which is documented somewhere. Compatible applications such as webviz-ert know how to use this variable and behave accordingly.

In the distant future applications could perhaps even register themselves, and then we can make sure that only ERT is able to write to the ert, ert3 ert.private etc namespaces. And webviz-ert can only read from ert and ert3.

Definition of done: POST and GET /userdata endpoints should use ?ns= (or make it part of the path) to select which namespace they're after. Namespaces are required parameters.