logs: log preset keys if preset not found

lib/datasource/npm/presets.js

@@ -14,6 +14,11 @@ async function getPreset(pkgName, presetName = 'default') {
   }
   const presetConfig = dep['renovate-config'][presetName];
   if (!presetConfig) {
+    const presetNames = Object.keys(dep['renovate-config']);
+    logger.info(
+      { presetNames, presetName },
+      'Preset not found within renovate-config'
+    );
     throw new Error('preset not found');
   }
   return presetConfig;