Adding a '--two-phase' option to 'pg_createsubscriber' utility.

Hi all,

I am writing to propose the addition of the two_phase option in
pg_createsubscriber. As discussed in [1], supporting this feature
during the development of pg_createsubscriber was planned for this
version.
Currently, pg_createsubscriber creates subscriptions with the
two_phase option set to false. Enabling the two_phase option after a
subscription has been created is not straightforward, as it requires
the subscription to be disabled first. This patch aims to address this
limitation by incorporating the two_phase option into
pg_createsubscriber which will help create subscription with two_phase
option and make use of the advantages of creating subscription with
two_phase option.
The attached patch has the changes for the same.

[1] - https://www.postgresql.org/message-id/CAA4eK1%2B7gRxiK3xNEH03CY3mMKxqi7BVz2k3VxxVZp8fgjHZxg%40mail.gmail.com

Thanks and regards,
Shubham Khanna.