Add Push Notification Plugin similar to LISTEN/NOTIFY in PostgreSQL

Hi, A good feature that PostgreSQL has is a way to enable PUSH Notifications in the client, so when a process need to update or send info to the client it can be done with this mechanism

Currently there no way to execute external commands to send info to an app, unless we use the https://github.com/mysqludf/lib_mysqludf_sys plugin, but this coudl lead to security issues, The PUSH Notification option could be a secure way to send messages to a certain client/app

This could be achieved by adding a plugin at server side and an addon DLL at client side
More info:

https://www.postgresql.org/docs/current/static/sql-listen.html

https://www.postgresql.org/docs/current/static/sql-notify.html