Time parameter in xAOD::TrackParticle

Up until now, the output of HGTD reconstruction has been a collection of xAOD::TrackParticle decorations conveying the HGTD timing information (with track and vertex times being derived from them post-reco). This MR is a first step towards a more integrated track time in the xAOD EDM.

The topic was discussed in a core software meeting, where a preliminary strategy was proposed to add the time as dynamic for now. This should make it relatively transparent for Run 3 code, but usable for upgrade code (in which case the time will still need to be set on every track).

/cc @akraszna @npetters @tadej @tstreble @ncalace @pagessin @lgagnon @aleopold