Method add_flag

simcore/framework/src/cli/cli.hpp:5234–5234

Add a flag with no description or variable assignment

 public:
  /// Add a flag with no description or variable assignment
  Option *add_flag(std::string flag_name) { return _add_flag_internal(flag_name, CLI::callback_t(), std::string{}); }

  /// Add flag with description but with no variable assignment or callback
  /// takes a constant string,  if a variable string is passed that variable will be assigned the results from the