Plan to commission HLT1 downstream reconstruction, vertexing, and selections

Triggered by the following discussion

!1198 (comment 7452713)

let's use this issue to make a plan for how best to commission the new HLT1 downstream reconstruction and figure out which additional components are required for this task. E.g. cut-based lines exploiting this new reconstruction as suggested by @lpica

@lpica @bjashal I let you tag everyone relevant here at your convenience