e11sync: add an optional 'database-path'

will be useful during deployment.

pkgs/e11sync.nix

@@ -1,5 +1,6 @@
 {
   self,
+  lib,
   stdenv,
   runCommand,
   makeWrapper,
@@ -8,6 +9,7 @@
   libmaxminddb,
   dart-sass,
   gunicornPort ? 8001,
+  database-path ? null,
   geoip-archive,
 }:
 stdenv.mkDerivation {
@@ -27,6 +29,9 @@ stdenv.mkDerivation {
     makeWrapper ${python3Packages.gunicorn}/bin/gunicorn $out/bin/e11sync-gunicorn \
       --chdir $out/app \
       --set-default E11SYNC_HTTP_PORT ${toString gunicornPort} \
+      ${lib.optionalString (database-path != null) ''
+        --set E11SYNC_DATABASE_PATH "${database-path}" \
+      ''} \
       --set E11SYNC_DEBUG "" \
       --set E11SYNC_COMPRESS_OFFLINE 1 \
       --set GEOIP_PATH "${geoip-archive}" \