Show Time to Baseline for each feature

**Is your feature request related to a problem? Please describe.**
For features that have reached Baseline status, it would be useful to show the time it took to get there. Getting broader awareness of that time will help the web ecosystem have a better understanding of the required investment and plan ahead for future efforts.

**Describe the solution you'd like**
The value would be the time between the feature shipping in one browser and the time it reaches Baseline Newly Available status. I think this would fit nicely in the Baseline box in the feature details page:


**Describe alternatives you've considered**
It may also be useful to display this as a separate column in the feature list view, so that sorting by that field could provide additional insights. Furthermore, if we end up storing this value in the database, it will be informative to display the average time for a feature to reach Baseline, both with its own indicator and also as an additional indication per feature (e.g.: `Time to Baseline: 6 months, 1 more than average`).

**Additional context**
The original idea came from Penny.