feat(storage): add runner script and docs for appendable upload benchmark

[vsharonlynn]

This PR comes after PR #6170.

Issue #5716.

[gemini-code-assist]

Code Review

This pull request introduces a new benchmark crate, storage-benchmark-appendable-object, to measure Google Cloud Storage appendable upload performance under various chunk sizes. The feedback suggests creating the output directory recursively before writing the CSV report to prevent potential runtime failures, and adding a lifecycle rule to the bucket setup instructions in the README to automatically delete uploaded objects and avoid unnecessary storage costs.

[gemini-code-assist]

Since each run of the benchmark uploads multiple large objects (e.g., 100 x 100 MiB = 10 GiB), these objects will accumulate in the zonal bucket and incur storage costs. It is highly recommended to configure a lifecycle rule on the bucket to automatically delete objects after 1 day.

Suggested change

	gcloud storage buckets create gs://${BUCKET_NAME} \
	--location=${ZONE} \
	--placement=zone \
	--default-storage-class=RAPID \
	--hierarchical-namespace \
	--uniform-bucket-level-access
	```
	gcloud storage buckets create gs://${BUCKET_NAME} \
	--location=${ZONE} \
	--placement=zone \
	--default-storage-class=RAPID \
	--hierarchical-namespace \
	--uniform-bucket-level-access
	# Add a lifecycle rule to delete objects after 1 day to avoid storage costs
	echo '{"rule": [{"action": {"type": "Delete"}, "condition": {"age": 1}}]}' > lifecycle.json
	gcloud storage buckets update gs://${BUCKET_NAME} --lifecycle-file=lifecycle.json
	rm lifecycle.json

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.59%. Comparing base (dec0817) to head (fa01ebe).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6171   +/-   ##
=======================================
  Coverage   96.58%   96.59%           
=======================================
  Files         266      266           
  Lines       66852    66852           
=======================================
+ Hits        64571    64574    +3     
+ Misses       2281     2278    -3     

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