buttons: Add TOPIC_INFO shortcut to TopicButton.

Author: srdeotarse

zulipterminal/ui_tools/buttons.py

@@ -349,6 +349,8 @@ def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
         if is_command_key("TOGGLE_TOPIC", key):
             # Exit topic view
             self.view.left_panel.show_stream_view()
+        elif is_command_key("TOPIC_INFO", key):
+            self.model.controller.show_topic_info(self.stream_id, self.topic_name)
         return super().keypress(size, key)