[FE] VSA - Add stage time to the horizontal stage items

Let's add the stage time for every stage to each item in the horizontal navigation.

• For the overview time, we should sum the time for all the other stages
• For stages with no / not enough data we should display a -
• We should ensure we summarise times accordingly
  • Use minute, hour, day, week & month units (example: less than minute == <1m)
  • Use one letter abbreviations (example: day == d)
  • On month and day timescales, it may be worth having 1 decimal place (example: 1.5d)
• Add related unit / feature specs