Update reservedNamespacesNames to include the name Symbol

[bassemmagdy]

An issue in desktop-wallet got raised as when a user try to create a namespace with the name symbol got an error: Failure_Namespace_Invalid_Duration as rest were trying to extend the namespace duration instead of creating a new one.
Expected result:
as symbol is one of the reservedNamespacesNames we expected Failure_Namespace_Root_Name_Reserved to be returned from rest same as the remaining reserved names in the list.