Added std::optional functionality to Gaudi::NamedRange

In order to optionally retrieve information from the event store the possibility of fetching an std::optional<Gaudi::NamedRange> was added -- because of the automatic conversion, fetching any Gaudi::NameRange happens by 'value', in order to insure the proper lifetime. As a result, one cannot fetch a Gaudi::NamedRange const* from the TES, and thus now the conversion code allows for std::optional< Gaudi::NamedRange> instead to provide the proper semantics.

The relevant example was to be able to enter and retrieve input id information of algorithms which will only exists if the algorithm ran, as decided by the control flow and therefore optional.