Build postgres using dockerfile

- use dockerfile to install postgis during build

hosts/common/optional/docker/postgres.nix

@@ -4,8 +4,16 @@
     backend = "docker";
     projects = {
       "db".settings.services."db".service = {
-        image = "postgres:16";
         restart = "unless-stopped";
+        build.context = "/nix/store";
+        build.dockerfile = builtins.baseNameOf "${pkgs.writeScript "pgDockerfile" ''
+            FROM postgres:16
+            # install packages
+            RUN apt-get update \
+                && apt-get install -y --no-install-recommends \
+                    postgresql-16-postgis \
+                && rm -rf /var/lib/apt/lists/*
+          ''}";
         environment = {
           POSTGRES_PASSWORD = "balls1234";
           POSTGRES_USER = "admin";