buttons: Add TOPIC_INFO shortcut to TopicButton.

Fixes zulip#1075.

Co-authored-by: Shivam Deotarse <[email protected]>

Author: rsashank

zulipterminal/ui_tools/buttons.py

@@ -381,6 +381,8 @@ def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
             # Exit topic view
             self.view.associate_stream_with_topic(self.stream_id, self.topic_name)
             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)