OpenAtlas » OpenAtlas Discovery

currently, we store configuration for network graph node colors in `project.config.json` (see https://github.com/acdh-oeaw/openatlas-discovery/blob/develop/project.config.json#L5-L22 and https://github.com/acdh-oeaw/openatlas-discovery/blob/develop/config/project.config.ts#L16-L33)

however, this file should only be used for configuration which is editable via cms.

we should either add the missing values to [`public/admin/config.yml`](https://github.com/acdh-oeaw/openatlas-discovery/blob/develop/public/admin/config.yml#L43-L54) if we want these colors to actually be user-configurable, or store them somewhere else (e.g. in `/config/network-visualisation.config.ts`) if they should not be user-configurable.

also, unrelated, this color (`rgb(400, 400, 400)`) does not make sense: https://github.com/acdh-oeaw/openatlas-discovery/blob/develop/project.config.json#L22