feat templater: Add IP lookup function

This introduces support for looking up IP addresses using local DNS resolver.

Function will return a list of all IP addresses associated with hostname.
Further processing can be achieved using supported list template functions.

templater/templater.go

@@ -180,6 +180,7 @@ func templateFuncs() template.FuncMap {
 		return string(b)
 	}
 	m["passLookup"] = GetFromPass
+	m["lookupIPAddr"] = GetIPsFromDNS
 
 	return m
 }