Add tool for fitting GN2 vertices

This MR implements a secondary vertex reconstruction algorithm based on the vertex groupings identified by GN2. This is implemented in the GNNVertexConstructorTool, and configured to run in the FTAG1 derivation via the GNNVertexConstructorAlg.

The main configurable parameter in the tool is HFRatio, which sets the threshold of tracks in a vertex grouping that have InDet::ExclusiveOrigin::FromB, InDet::ExclusiveOrigin::FromBC, or InDet::ExclusiveOrigin::FromC, as identified from the track classification of GN2. Additional selections on the vertex fit chi2 and radial position are configurable via tool properties. The algorithm currently creates a new xAOD::VertexContainer, and adds links from this container onto the jet objects.

Tagging @svanstro @pgadow @hartman @dguest @fdibello