Initial plan for hiding Change template button when <=1 template

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

src/@types/vscode.proposed.chatSessionsProvider.d.ts

@@ -241,6 +241,14 @@ declare module 'vscode' {
 		 */
 		readonly onDidChangeChatSessionOptions?: Event<ChatSessionOptionChangeEvent>;
 
+		/**
+		 * Event that the provider can fire to signal that the available provider options have changed.
+		 *
+		 * When fired, the editor will re-query {@link ChatSessionContentProvider.provideChatSessionProviderOptions}
+		 * and update the UI to reflect the new option groups.
+		 */
+		readonly onDidChangeChatSessionProviderOptions?: Event<void>;
+
 		/**
 		 * Provides the chat session content for a given uri.
 		 *