Add a command line option to enable and list extensions (#3191)

packages/cli/src/gemini.tsx

@@ -103,6 +103,14 @@ export async function main() {
   const extensions = loadExtensions(workspaceRoot);
   const config = await loadCliConfig(settings.merged, extensions, sessionId);
 
+  if (config.getListExtensions()) {
+    console.log('Installed extensions:');
+    for (const extension of extensions) {
+      console.log(`- ${extension.config.name}`);
+    }
+    process.exit(0);
+  }
+
   // Set a default auth type if one isn't set for a couple of known cases.
   if (!settings.merged.selectedAuthType) {
     if (process.env.GEMINI_API_KEY) {