Datadog integration

[ibrahimcesar]

Description

Export telemetry data to Datadog for teams using their observability platform.

Features

• Datadog Logs integration
• Custom metrics export
• Trace correlation
• Dashboard templates

Example Usage

```rust
TelemetryKit::builder()
.service_name("my-app")
.with_datadog(DatadogConfig {
api_key: env::var("DD_API_KEY")?,
site: "datadoghq.com",
})
.build()?;
```

Benefits

• Use existing Datadog investment
• Unified observability view
• Advanced analytics capabilities

Acceptance Criteria

• Optional datadog feature flag
• Efficient batched export
• Datadog tagging support