Include VTK in CI "full" builds
Currently, the CI "full" builds of Nektar++ do not build with VTK enabled. If we want to ensure that the code can be built successfully with VTK enabled, this should be included.
The NEKTAR_USE_VTK=ON
option needs to be added to the main CI build/test script and relevant vtk packages need to be added to the package list files for each distro.