Global and snapshot configuration elements

[riban-bw]

Is your feature request related to a problem? Please describe.
There are some configuration elements that should apply globally and not change when a snapshot is recalled. There are others that should be recalled from a snapshot and others that should be recalled from a zs3. There is overlap of these sets of configuration that different user workflows may require different behaviour.

Describe the solution you'd like
Consolidate the configuration into a single, consistent format. (Currently stored in files, envvars, etc.)
Have a set of configuration that are global and not saved in snapshot.
Have a set of configuartion that are set in snapshot.
Have a set of configuartion that are set in zs3.
Identify configurations that may be beneficial to store in zs3/snapshot/global. Add a mechanism to flag these to indicate where they are stored and/or restored.

Describe alternatives you've considered
Resave all ZS3 & sanpshots when a setting has changed due to workflow change.

Additional context
An example of where you might want to store a configuration differently, depending on workflow is mentioned in #1279. The tools to decide whether options should be stored in / recalled from zs3/snapshot need to be simple, maybe listbox accessible via zs3/snapshot context menus and ideally also in webconf.

State is stored in snapshot in json matching the state schema. This could be expanded so that the snapshot is a branch of the full configuration including global configuration - or an overlay so that saved elements may be restored over existing ones and non-saved elements don't change value on recall.