The basic replication mechanisms have been built-in for quite a while. What’s not there is cluster management (replica launching, leader election, load balancing, that sort of thing) that makes it practical in a nontrivial situation. There are several 3rd party solutions to that. [0]

Same situation as, e.g., backups. You can just use pg_dump, but to be serious you need a 3rd party solution that does log shipping and so on.

[0] https://www.postgresql.org/download/products/3-clusteringrep...