Motivation for this change

Postgresql-12 is out !

This PR adds it.

I had to change the pgdumpOptions in he dump service test since in pg_12, pg_dump does not have a -o|--oids option anymore. I think the default option of the service should be changed to -Cb to avoid this problem for people using postgresql_12, but for the time being, I have only changed it in the test.

cc @zagy

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @