fix: allow config directory to be configurable

For postgres, the config directory doesn't actually exist, so adding this configurability allows the plugin's info command to report correctly.

common-functions

@@ -383,7 +383,7 @@ service_info() {
   local flag key valid_flags
 
   local flag_map=(
-    "--config-dir: ${SERVICE_ROOT}/config"
+    "--config-dir: ${SERVICE_ROOT}/${PLUGIN_CONFIG_SUFFIX}"
     "--data-dir: ${SERVICE_ROOT}/data"
     "--dsn: ${SERVICE_URL}"
     "--exposed-ports: $(service_exposed_ports "$SERVICE")"