Make Dangerbot add approval groups to MRs based on heuristic rules
### Problem to solve
Sometimes we merge MRs that haven't gotten the proper approvals.
In order to try and make clearer when MRs need gitlab-ce~2492649, gitlab-ce~3412464 and/or ~ux review by a maintainer, it was discussed in the ~Create monthly to try some rules out via Danger.
By following a few rules, we can come up with scenarios where confidence on setting Blocking Approval Groups is high enough.
**Please discuss below rules to require approvals from which groups:**
*Eg.: If an MR has gitlab-ce~10230929 and/or touches `/app/`, require 1x approval from each group: gitlab-ce~2492649 gitlab-ce~3412464 gitlab-ce~2024184.*
### Further details
More on <a href="https://docs.gitlab.com/ee/user/project/merge_requests/merge_request_approvals.html">Merge Request Approvals</a>.
### Proposal
Danger bot checks a set of rules and applies corresponding groups requiring at least 1x approval from each.
### Testing
It might happen that the wrong approval groups are set initially, so we can maybe start with a simple suggestion in the comment.
### What does success look like, and how can we measure that?
The decrease in number of times MRs are inadvertently merged missing one or more required approvals.
### Links / references
issue