Service to manage derived signals.

A derived signal is a DSL expression with a unique label. The label must be unique to the customer.

Derived signals are stored in Library folders and shared across users through folder sharing.

Requests to the DerivedSignalService are executed in the context of the customer's service account (SA). The SA is a special user that is a member of the customer user group, giving it access to all folders that are shared with this user group, but not to private folders. Hence, only derived signals that are in folders shared to the SA, via the customer user group, will be accessible via the DerivedSignalService.