pg_recvlogical cannot create slots with failover=true

Dear hackers,

While reviewing threads I found $SUBJECT.

I think it does not affect to output, but I could not find strong reasons not to
support it. Also, this can be used for testing purpose, i.e., DBAs can verify the
slot-sync can work on their system by only using pg_recvlogical.

Attached patch implements it. Since -f/-F option has already been used, -O was
chosen for the short-version. Better idea is very welcomed.

How do you feel?

Best regards,
Hayato Kuroda
FUJITSU LIMITED