docs(bigquery): add sample for restoring multiple deleted tables

[alihanoz-google]

Description

This PR adds a Python sample script demonstrating how to programmatically find and restore multiple deleted BigQuery tables concurrently using INFORMATION_SCHEMA.TABLE_STORAGE, time travel decorators, and ThreadPoolExecutor.

Fixes #14641

Checklist

Testing

• I have tested this change on a live environment and verified it works as intended.

Compliance & Style

• I have followed the Sample Guidelines.
• The README is updated with all relevant information (if applicable).
• If this PR adds a new sample directory: I updated the CODEOWNERS file.

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Post-Approval Actions

• Please merge this PR for me once it is approved

[snippet-bot]

Here is the summary of changes.

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• bigquery/cloud-client/restore_multiple_tables.py:19, tag bigquery_restore_multiple_tables

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[gemini-code-assist]

Code Review

This pull request introduces a new script restore_multiple_tables.py to restore multiple deleted BigQuery tables concurrently using time travel. A security issue was identified regarding potential SQL injection when interpolating dataset_id into the query string, and it is recommended to use parameterized queries instead.