Validate subscription conninfo on owner change

Validate subscription conninfo on owner change

For subscriptions using SERVER, changing the owner can change the
effective connection string. However, ALTER SUBSCRIPTION ... OWNER TO
did not validate the generated conninfo for the new owner.

As a result, ownership could be transferred to a non-superuser whose
generated connection string did not satisfy password_required=true.
The ownership change succeeded, but the subscription would fail later
when the worker or another command tried to connect.

Fix this by making ALTER SUBSCRIPTION ... OWNER TO validate the new
owner's generated conninfo with walrcv_check_conninfo().

Backpatch to v19, where SERVER subscriptions were introduced.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Yuanchao Zhang <145zhangyc@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://postgr.es/m/CAHGQGwFGa6+wWVgUmZPFwN=fBY59mYPkMK3=TxT=Pv5C1mNNRQ@mail.gmail.com
Backpatch-through: 19