Add new endpoints /api/v1/stats

[pinkwah]

This endpoint should expose:

1. The total number of simulations performed (all-time, 30d, 7d, 24h)
2. The number of simulations per adapter (all-time, 30d, 7d, 24h)
3. Number of failed simulations

We can do this by counting results in the database. This should be cached.

This will primarily be used on the home-page as a fun-fact, as well as our team's Grafana instance.