chore: sample for opentelemetry traces

[surbhigarg92]

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[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• examples/trace.py:33, tag spanner_opentelemetry_traces_cloudtrace_usage
• examples/trace.py:49, tag spanner_opentelemetry_traces_otlp_usage

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