List the update definitions available for a storage server that is a registered component
of the specified system. The storage server must be a component of the system; if it is not,
the request returns 404.

This is a read-only operation. The updateDefinitions array may be empty when no updates have
been synced for the storage server's type by its provider/plugin (for example, an array-firmware
integration that has not yet discovered an available version) — an empty list is a normal result,
not an error.