add eTLD validation support

[tarunKoyalwar]

Description

usually eTLD's don't resolve to ip . since its general use case is to act like TLD however lot of orgs host services on eTLD.
Example below are eTLD and some of them have resolve which some not

echo -e "ngrok.io\nco.uk\nai" | dnsx -resp

      _             __  __
   __| | _ __   ___ \ \/ /
  / _' || '_ \ / __| \  / 
 | (_| || | | |\__ \ /  \ 
  \__,_||_| |_||___//_/\_\

		projectdiscovery.io

[INF] Current dnsx version 1.1.4 (latest)
ngrok.io [34.210.2.84] 
ai [209.59.119.34] 

ValidateFQDN function used for validation of root domains does not consider this use case which classifies ngrok.io and ai as invalid domains here but some of them are valid (ex: http://ai 😆 )

Proposed Changes

• for proper validation check if given domain is eTLD if so try to resolve it using retryabledns if resolved then it is considered as valid domain if not then it is suffix(i.e not valid for this repo)

[tarunKoyalwar]

ref: https://stackoverflow.com/questions/69614892/can-a-domain-consist-of-only-tld-top-level-domain