postgresqlPackages.postgis: build minimal gdal version

This change is reducing closure size from 1.5G to
544M.

nixos/tests/postgis.nix

@@ -24,6 +24,7 @@ import ./make-test-python.nix ({ pkgs, ...} : {
     master.wait_for_unit("postgresql")
     master.sleep(10)  # Hopefully this is long enough!!
     master.succeed("sudo -u postgres psql -c 'CREATE EXTENSION postgis;'")
+    master.succeed("sudo -u postgres psql -c 'CREATE EXTENSION postgis_raster;'")
     master.succeed("sudo -u postgres psql -c 'CREATE EXTENSION postgis_topology;'")
   '';
 })

pkgs/servers/sql/postgresql/ext/postgis.nix

@@ -5,7 +5,7 @@
 , postgresql
 , geos
 , proj
-, gdal
+, gdalMinimal
 , json_c
 , pkg-config
 , file
@@ -14,6 +14,10 @@
 , pcre2
 , nixosTests
 }:
+
+let
+  gdal = gdalMinimal;
+in
 stdenv.mkDerivation rec {
   pname = "postgis";
   version = "3.4.1";