[WIP] Adding Documentation for Enabling External Authentication - Depends on External auth3 pull request.

Adding ManageIQ/Guides for installing and enabling
external authentication via IPA.

Depends on the External auth3 Pull Request https://github.com/ManageIQ/manageiq/pull/32


The IPA Server serves as the test.company.com domain
controller, Kerberos server, and as the LDAP DIT, hosting
the Root DSE dc=test,dc=company,dc=com.