Add VTK support to Linux CI full builds and to Nektar Docker image build config

This MR modifies the CI configuration to add NEKTAR_USE_VTK=ON to the "full" CI build config. It also adds the VTK dev package dependency to the full build package list for each of the distrubutions that we build for under the CI system.

Currently this MR supports only the Linux builds of Nektar++. Further work will be required for macOS and to see if we can also provide support for Windows 10.