Add changelog

Documentation/release/dev/add-catalyst-module.md

+## Add VTK::catalyst module
+
+VTK now has a new module called `VTK::catalyst` which is enabled with VTK_ENABLE_CATALYST,
+It looks for an external Catalyst installation and exposes catalyst's CMake functionality.
+Other VTK modules, such as `VTK::IOCatalystConduit`, can now depend on `VTK::catalyst` instead
+of trying to find the Catalyst package themselves.