[AUR-408] Export logs to Excel (#23)

This CL implements:

- The logic to export log to Excel.
- Route the export logic in the UI.
- Demonstrate this functionality in `./examples/promptui` project.

setup.py

@@ -35,6 +35,7 @@ setuptools.setup(
         "llama-hub",
         "nltk",
         "gradio",
+        "openpyxl",
     ],
     extras_require={
         "dev": [