For being able to use e.g. "-v" to use TCP communication with the NSUPDATE_SERVER -> NSUPDATE_OPT has been added.
NSUPDATE_OPT will be plainly added to the command line of nsupdate.
NSUPDATE_OPT will also be saved to conf respectively read from conf
https://domains.google/learn/gts-acme/
This is an ACME API for Google Domains customers, which is
different from the Google Cloud Domains API for Google Cloud
customers.