doc/nixos/postgress: Mention extensions in upgrading
doc/nixos/postgress: Mention extensions in upgrading

analyze_new_cluster script is not available in PostgreSQL 14+:

https://github.com/postgres/postgres/commit/8f113698b63b15a4e0a4b15d3ee37238c1d1821d

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs