R1:7a39ac43b48c

Add a "list<regex>" config option and move regex config to it

Summary:
Fixes T3807. Several issues:

- Currently, we split config of type `list<string>` on commas, which makes it impossible to enter a regex with a comma in it.
- Split on newlines only.
- Some of the examples are confusing (provided in JSON instead of the format you actually have to enter them).
- Show examples in the same format you should enter text.
- We didn't validate regexps.
- Introduce `list<regex>` to validate…