Insights: update live preview for scoped-repo-list insights to indicate you get 12 points but can preview 7

Created by: Joelkw

Per Alicja's comment/suggestions here:

1. Show 7 datapoints
2. Show the full timeframe, and show 5 additional datapoints faded out/suggested

Design

• Figma
• Changes to make:
  • add an opaque overlay over missing points (with stipes)
  • dashed line between missing data points