feat(tracing-spans): add otel.kind = "client" for OpenTelemetry compatibility

[uuushiro]

Summary

This PR adds otel.kind = "client" to the db_span! macro, ensuring DB spans are properly recognized as Client spans by OpenTelemetry-compatible APM tools.

Problem

When using tracing-opentelemetry as the bridge between tracing and OpenTelemetry, DB spans created by sea-orm are not recognized as database client calls because:

• tracing-opentelemetry uses the otel.kind field to determine SpanKind
• Without this field, spans default to SpanKind::Internal
• APM tools (Datadog, Jaeger, etc.) use SpanKind::Client + db.system attribute to identify DB operations

Solution

Add otel.kind = "client" to the db_span! macro. This is the documented approach for setting SpanKind via tracing spans.

Changes

::tracing::info_span!(
    $name,
    otel.kind = "client",  // Added
    db.system = ...,
    db.operation = ...,
    ...
)

[tyt2y3]

sorry I missed this

[github-actions]

🎉 Released In 2.0.0-rc.35 🎉

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