Combine all Minder PR comments into a single comment

[eleftherias]

When a new PR comment is added, we should combine it with existing comments from other rules, rather than having Minder create separate comments for each rule.

Out of scope:

• Gitlab

[evankanderson]

@ethomson points out a concern about rule evaluations completing on different time schedules:

If license scanning takes 100ms and static analysis takes 5 minutes, do we add the license scan report right away and then update the comment later when static analysis comes in?