OptionalAvailableConfigures what content types are available to the user. This includes dropdown list of the "+ Add" button and wether the user can drag&drop files.
Example:
{
"AvailableContentTypes": ["Folder", "File document"]
}
Multi-language Example:
{
"AvailableContentTypes": ["Folder", "File document", "Složka", "Dokument spisu"]
}
Configuration related to the SharePoint list shown as a side-content when the user is within a folder.