`milestone-was-set` judge missing for reading and creating facts for milestones

Let's implement a new judge that will read all milestones and create facts for each of them:

```
what: milestone-was-set
milestone: 333
when: 2024-01-01 (when it was set)
deadline: 2025-03-03 (when is the milestone)
who: 888 (who set it)
```