docs(spanner): snippet for setting read lock mode

[skuruppu]

Snippet shows how to set the read lock mode at the client-level and how to override the option at the transaction-level.

[snippet-bot]

Here is the summary of changes.

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• samples/samples/snippets.py:3241, tag spanner_read_lock_mode

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[gemini-code-assist]

Summary of Changes

Hello @skuruppu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new code example for Google Cloud Spanner, focusing on the configuration of read lock modes within read-write transactions. The added snippet provides clear guidance on how to apply read lock settings both globally at the client level and specifically for individual transactions, enhancing flexibility for developers managing concurrency. This change improves the documentation and usability of Spanner's transaction options.

Highlights

• New Snippet for Read Lock Mode: A new Python snippet, read_lock_mode_options, has been added to demonstrate how to configure read lock modes for Google Cloud Spanner read-write transactions.
• Client-Level Configuration: The snippet illustrates setting a default read lock mode (e.g., OPTIMISTIC) at the Spanner client level, which applies to all subsequent read-write transactions.
• Transaction-Level Override: It also shows how to override the client-level read lock mode with a different mode (e.g., PESSIMISTIC) for a specific transaction, providing granular control.
• Snippet Integration and Testing: The new snippet has been integrated into the command-line interface for snippets.py and includes a corresponding unit test in snippets_test.py to ensure its functionality.

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[gemini-code-assist]

Code Review

This pull request introduces a new snippet to demonstrate setting the read lock mode for Spanner transactions, both at the client and transaction level. The changes include the new snippet function, its command-line integration, and a corresponding unit test. The implementation is sound, but there's a minor style issue regarding the placement of the docstring in the new function, which I've commented on.

[skuruppu]

@rahul2393 sorry for the trouble, I need your approval again as I made some small changes that were suggested by Gemini.

Please feel free to merge when you're ready.