feat(spanner): add change streams transaction exclusion sample

[ShuranZhang]

Add sample for how to configure change streams transaction exclusion option for a read write transaction.

I don't have access to re-open #4108, this is basically a duplicate.

[snippet-bot]

Here is the summary of changes.

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• spanner/spanner_snippets/spanner/spanner_change_streams_txn_exclusion.go:17, tag spanner_set_exclude_txn_from_change_streams

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[code-review-assist]

Hi team,

I'm currently reviewing this pull request and will provide my feedback shortly. In the meantime, here's a summary for you and other reviewers to quickly get up to speed:

This pull request, authored by ShuranZhang, aims to add a sample demonstrating how to configure the transaction exclusion option for change streams in Spanner read-write transactions. Specifically, it adds a new sample that shows how to exclude a read-write transaction from being tracked by change streams.

Here's a breakdown of the changes:

• New File: spanner/spanner_snippets/spanner/spanner_change_streams_txn_exclusion.go This file contains the new sample code that demonstrates how to exclude a read-write transaction from change streams using spanner.TransactionOptions{ExcludeTxnFromChangeStreams: true}. The code inserts and updates a row in the Singers table within a transaction, and then prints confirmation messages to the console.
• Modified File: spanner/spanner_snippets/spanner/integration_test.go This file has been updated to include a test case for the new rwTxnExcludedFromChangeStreams function (lines 437-443). This test verifies that the transaction is correctly excluded from change streams by asserting that specific messages are present in the output.

The changes are well-structured and clearly demonstrate the intended functionality. The comments are helpful and the code is easy to follow.

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And now, a little haiku to lighten the mood:

Streams flow, data bright,
Transactions, neatly kept,
Code review's delight.

Thanks,
Gemini

[code-review-assist]

The sample demonstrates how to exclude read-write transactions from change streams. The code is well-structured and easy to understand. The PR description could be improved by adding a link to the documentation.