Add a test for `CONFIGURE INSTANCE SET listen_addresses` (#2718)
Add a test for `CONFIGURE INSTANCE SET listen_addresses` (#2718)

Test that changing the `listen_addresses` set does not affect existing
connections and that the new address is immediately available for new
connections.

Co-authored-by: Łukasz Langa <6c5eb78e54fa6aff67ba440c4bd5b1e43956c922@langa.pl>
Closes: #1298

Co-authored-by: Łukasz Langa <6c5eb78e54fa6aff67ba440c4bd5b1e43956c922@langa.pl>
edgedb/edgedb,edgedb/edgedb,edgedb/edgedb