feat(cli): add hideBanner setting to disable startup banner (#2803)

Co-authored-by: Pascal Birchler <pascalb@google.com>

packages/cli/src/config/settings.ts

@@ -79,6 +79,7 @@ export interface Settings {
   // UI setting. Does not display the ANSI-controlled terminal title.
   hideWindowTitle?: boolean;
   hideTips?: boolean;
+  hideBanner?: boolean;
 
   // Setting for setting maximum number of user/model/tool turns in a session.
   maxSessionTurns?: number;