feat: add stagingquery quickstart for purchases (#375)

## Summary

## Checklist
- [ ] Added Unit Tests
- [ ] Covered by existing CI
- [ ] Integration tested
- [ ] Documentation update
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Introduced a new query to retrieve purchase records with date range
filtering.
- Enhanced data retrieval by including additional contextual metadata
for improved insights.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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---------

Co-authored-by: Thomas Chow <[email protected]>

Author: tchow-zlai

api/py/test/sample/staging_queries/quickstart/purchases.py

@@ -0,0 +1,38 @@
+#     Copyright (C) 2023 The Chronon Authors.
+#
+#     Licensed under the Apache License, Version 2.0 (the "License");
+#     you may not use this file except in compliance with the License.
+#     You may obtain a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#     Unless required by applicable law or agreed to in writing, software
+#     distributed under the License is distributed on an "AS IS" BASIS,
+#     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#     See the License for the specific language governing permissions and
+#     limitations under the License.
+
+from ai.chronon.api.ttypes import StagingQuery, MetaData
+
+
+
+query = """
+SELECT
+    ts,
+    ds,
+    purchase_id,
+    user_id,
+    product_id,
+    purchase_price
+FROM data.purchases
+WHERE ds BETWEEN '{{ start_date }}' AND '{{ end_date }}'
+"""
+
+staging_query = StagingQuery(
+    query=query,
+    startPartition="2023-10-31",
+    metaData=MetaData(
+        name='purchases_staging_query',
+        outputNamespace="data"
+    )
+)