postgresql_13: drop as it's EOL (#462543)

- `postgresql` and `libpq` don't provide `pg_config` by default anymore. Instead, `pg_config` is available via `postgresql.pg_config` or `libpq.pg_config`. This allowed implementing it as a shell script, which can be built for both the build and host systems when cross-compiling. If your build fails to find `pg_config`, add `postgresql.pg_config` or `libpq.pg_config` to `nativeBuildInputs`.

- `postgresql_13` has been removed since it reached its end of life.

- The [`no-broken-symlinks` hook](https://nixos.org/manual/nixpkgs/unstable/#no-broken-symlinks.sh) was added to catch builds containing dangling or reflexive symlinks, as these are indicative of problems with packaging.

  The hook can be disabled by providing `dontCheckForBrokenSymlinks = true;` as an argument to `mkDerivation`.

  For more information, [check the docs](https://nixos.org/manual/nixpkgs/unstable/#no-broken-symlinks.sh) or [see this PR](https://github.com/NixOS/nixpkgs/pull/370750).

## Upgrading {#module-services-postgres-upgrading}

::: {.note}

The steps below demonstrate how to upgrade from an older version to `pkgs.postgresql_13`.

The steps below demonstrate how to upgrade from an older version to `pkgs.postgresql_15`.

These instructions are also applicable to other versions.

:::

NixOS places the state into {file}`/var/lib/postgresql/<version>` where each `version`

can be obtained like this:

```

$ nix-instantiate --eval -A postgresql_13.psqlSchema

"13"

$ nix-instantiate --eval -A postgresql_15.psqlSchema

"15"

```

For an upgrade, a script like this can be used to simplify the process:

```nix

      let

        # XXX specify the postgresql package you'd like to upgrade to.

        # Do not forget to list the extensions you need.

        newPostgres = pkgs.postgresql_13.withPackages (pp: [

        newPostgres = pkgs.postgresql_15.withPackages (pp: [

          # pp.plv8

        ]);

        cfg = config.services.postgresql;

  2. Login as root (`sudo su -`).

  3. Run `upgrade-pg-cluster`. This will stop the old postgresql cluster, initialize a new one and migrate the old one to the new one. You may supply arguments like `--jobs 4` and `--link` to speedup the migration process. See <https://www.postgresql.org/docs/current/pgupgrade.html> for details.

  4. Change the postgresql package in NixOS configuration to the one you were upgrading to via [](#opt-services.postgresql.package). Rebuild NixOS. This should start the new postgres version using the upgraded data directory and all services you stopped during the upgrade.

  5. After the upgrade it's advisable to analyze the new cluster:

       - For PostgreSQL ≥ 14, use the `vacuumdb` command printed by the upgrades script.

       - For PostgreSQL < 14, run (as `su -l postgres` in the [](#opt-services.postgresql.dataDir), in this example {file}`/var/lib/postgresql/13`):

         ```

         $ ./analyze_new_cluster.sh

         ```

     ::: {.warning}

     The next step removes the old state-directory!

     :::

     ```

     $ ./delete_old_cluster.sh

     ```

  5. After the upgrade it's advisable to analyze the new cluster with the `vacuumdb` command printed by the upgrades script.

## Versioning and End-of-Life {#module-services-postgres-versioning}

            pkgs.postgresql_16

          else if versionAtLeast config.system.stateVersion "23.11" then

            pkgs.postgresql_15

          else if versionAtLeast config.system.stateVersion "22.05" then

            pkgs.postgresql_14

          else

            pkgs.postgresql_13

            pkgs.postgresql_14

        '';

        description = ''

          The package being used by postgresql.

          else if versionAtLeast config.system.stateVersion "22.05" then

            pkgs.postgresql_14

          else if versionAtLeast config.system.stateVersion "21.11" then

            mkWarn "13" pkgs.postgresql_13

            mkThrow "13"

          else if versionAtLeast config.system.stateVersion "20.03" then

            mkThrow "11"

          else if versionAtLeast config.system.stateVersion "17.09" then

            };

            postgresql = {

              enable = true;

              package = pkgs.postgresql_13;

              package = pkgs.postgresql_14;

            };

            nginx = {

              enable = true;

  # version. In other words: Do not remove the second-to-last minor version from nixpkgs,

  # yet. Update first.

  versions = {

    postgresql_13 = ./13.nix;

    postgresql_14 = ./14.nix;

    postgresql_15 = ./15.nix;

    postgresql_16 = ./16.nix;