[SSSD] INI validation design page for review

[Dmitri Pal]

Hi,

Added the following page:
https://fedorahosted.org/sssd/wiki/WikiPage/INIFileValidatorDesign

This is significant effort, I should say...
Will be quite a headache. I wonder is it really worth it at this point?

IMO I would prefer switching to ELAPI and bringing it into a decent
shape and then get back to this in half a year...