chore: samples for opentelemetry tracing

[surbhigarg92]

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[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• samples/observability-traces-otlp.js:28, tag spanner_opentelemetry_traces_otlp_usage
• samples/observability-traces.js:28, tag spanner_opentelemetry_traces_cloudtrace_usage

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[generated-files-bot]

Warning: This pull request is touching the following templated files:

• README.md - README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml
• samples/README.md - samples/README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml