Render default/current settings in the same format they'll be edited

Summary:
Fixes T4773. For config settings of type `list<string>`, `set`, or `list<regex>`, the "defaults" table and "examples" aren't always in the same format you should actually use when changing the setting.

This is pretty confusing. Instead, always show the settings in the desired format. For example, if the user should enter a newline-separated list, show them a newline separated list.

Test Plan:
  - Grepped for `list<string>`, `list<regex>`, and `'set'`; verified all the config had the right example format (most already did).
  - Viewed config settings of various kinds, including custom settings.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4773

Differential Revision: https://secure.phabricator.com/D8725