Add missing include to #include <boost/mpl/vector.hpp>

[Tobias-Fischer]

Fixes:

$SRC_DIR/ros-noetic-rosmon-core/src/work/src/launch/substitution_python.cpp: In function 'boost::python::api::object rosmon::launch::make_handler(F)':
$SRC_DIR/ros-noetic-rosmon-core/src/work/src/launch/substitution_python.cpp:32:29: error: 'vector' is not a member of 'boost::mpl'; did you mean 'vector'?
   32 |                 boost::mpl::vector<std::string, const std::string&>()
      |                             ^~~~~~
      |                             vector9

[xqms]

Thanks!