Add the "Security" config group options.

Summary: Added all the "Security" group options listed in T2255.

Test Plan:
- Looked at all the options.
- Tested validation on `security.alternate-file-domain`

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4334