chore(spanner): add sample codes and sample ITs for Cloud Spanner Queues.

[finnzzf]

Adding sample codes and tests for queues.

[gemini-code-assist]

Code Review

This pull request introduces a new QueueSample class and its corresponding integration test QueueSampleIT to demonstrate Spanner queue operations, including database creation, sending, receiving, acknowledging, and deleting messages using both Mutation and SQL APIs. The review feedback suggests improving exception handling in the sample code by propagating exceptions in createQueueDatabase instead of catching and swallowing them, which simplifies the code and ensures failures are properly propagated.

[rahul2393]

We don't have any sample tags here?

[snippet-bot]

Here is the summary of changes.

You are about to add 9 region tags.

• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:40, tag spanner_create_database_with_queue
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:58, tag spanner_send_to_queue_with_mutation_api
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:71, tag spanner_send_to_queue_with_sql_api
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:84, tag spanner_send_to_queue_with_mutation_api_in_future
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:99, tag spanner_send_to_queue_with_sql_api_in_future
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:115, tag spanner_ack_queue_message_with_mutation_api
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:127, tag spanner_ack_queue_message_with_sql_api
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:140, tag spanner_delete_queue_message_with_sql_api
• java-spanner/samples/snippets/src/main/java/com/example/spanner/QueueSample.java:153, tag spanner_send_and_receive_queue_message_with_sql_api

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[rahul2393]

Ok when we add tag we make sure that tags are common across all languages so that in future if we write a cloud doc and try to link sample they all can get linked

I see in python we have sparate sets of tags then here https://github.com/finnzzf/google-cloud-python/blob/main/packages/google-cloud-spanner/samples/samples/queue_snippets.py, do we have agreement on how we will be showcasing this?