move playground ui to llama-stack repo (#536)

# What does this PR do?

- Move Llama Stack Playground UI to llama-stack repo under
llama_stack/distribution
- Original PR in llama-stack-apps:
https://github.com/meta-llama/llama-stack-apps/pull/127

## Test Plan
```
cd llama-stack/llama_stack/distribution/ui
streamlit run app.py
```


## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [ ] Ran pre-commit to handle lint / formatting issues.
- [ ] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

llama_stack/distribution/ui/modules/utils.py

@@ -0,0 +1,31 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+import os
+
+import pandas as pd
+import streamlit as st
+
+
+def process_dataset(file):
+    if file is None:
+        return "No file uploaded", None
+
+    try:
+        # Determine file type and read accordingly
+        file_ext = os.path.splitext(file.name)[1].lower()
+        if file_ext == ".csv":
+            df = pd.read_csv(file)
+        elif file_ext in [".xlsx", ".xls"]:
+            df = pd.read_excel(file)
+        else:
+            return "Unsupported file format. Please upload a CSV or Excel file.", None
+
+        return df
+
+    except Exception as e:
+        st.error(f"Error processing file: {str(e)}")
+        return None