feat(spanner): migrate batch 3 core samples and tests

[angelcaamal]

Description

Fixes Internal: b/498728370

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[snippet-bot]

Here is the summary of changes.

You are about to add 16 region tags.

• spanner/add-and-drop-new-database-role.js:26, tag spanner_add_and_drop_database_role
• spanner/create-instance-without-default-backup-schedules.js:20, tag spanner_create_instance_without_default_backup_schedule
• spanner/get-database-roles.js:26, tag spanner_list_database_roles
• spanner/instance-update.js:24, tag spanner_update_instance
• spanner/instance-with-asymmetric-autoscaling-config.js:24, tag spanner_create_instance_with_asymmetric_autoscaling_config
• spanner/instance-with-autoscaling-config.js:24, tag spanner_create_instance_with_autoscaling_config
• spanner/instance-with-processing-units.js:19, tag spanner_create_instance_with_processing_units
• spanner/instance.js:20, tag spanner_create_instance
• spanner/read-data-with-database-role.js:26, tag spanner_read_data_with_database_role
• spanner/read-lock-mode.js:26, tag spanner_read_lock_mode
• spanner/repeatable-reads.js:26, tag spanner_isolation_level
• spanner/request-tag.js:23, tag spanner_set_request_tag
• spanner/statement-timeout.js:23, tag spanner_set_statement_timeout
• spanner/transaction-tag.js:23, tag spanner_set_transaction_tag
• spanner/transaction-timeout.js:23, tag spanner_transaction_timeout
• spanner/update-instance-default-backup-schedule-type.js:24, tag spanner_update_instance_default_backup_schedule_type

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[gemini-code-assist]

Code Review

This pull request introduces a comprehensive set of Node.js code samples for Google Cloud Spanner, including database role management, instance configuration (autoscaling, processing units, backup schedules), and advanced transaction settings like isolation levels, lock modes, and tags. Additionally, it enables numerous integration tests that were previously disabled. I have no feedback to provide.