RUMM-295 Add logs to spans

[ncreated]

What and why?

📦 With this PR it is possible to send logs from a span:

let dataDownloadingSpan = tracer.startSpan(
    operationName: "data downloading",
    childOf: viewAppearingSpan.context
)

// Simulate logging download progress
dataDownloadingSpan.log(
    fields: [
        "message": "download progress",
        "progress": 0.99
    ]
)

dataDownloadingSpan.finish()

How?

Technically, logs are linked to the span by the server, when this two internal attributes are provided:

static let traceID = "dd.trace_id"
static let spanID = "dd.span_id"

With small refactoring, I was able to fully reuse the Logging feature from DDTracer 🏅. The thin features integration layer was introduced:

internal struct TracingToLoggingOutput {
    /// `LogOutput` provided by the `Logging` feature.
    let loggingOutput: LogOutput

    func writeLogWith(spanContext: DDSpanContext, fields: [String: Encodable], date: Date) {
       // ... prepare the log ...
       loggingOutput.writeLogWith(level: .info, message: message, date: date, attributes: logAttributes, tags: [])
    }
}

I've put this TracingToLoggingOutput in FeaturesIntegration group, so we separate both features on the project level:

Because now the Tracing feature uses the storage stack from the Logging feature, it was reflected in the TracingFeature initializer ✨:

// TracingFeature

init(
    directory: Directory,
    configuration: Datadog.ValidConfiguration,
    performance: PerformancePreset,
+    loggingFeatureStorage: LoggingFeature.Storage,
    mobileDevice: MobileDevice,
    httpClient: HTTPClient,
) { /* ... */ }

Refactoring

This integration required a refactoring of the Logging feature, so that the log date is no longer created by the LogBuilder. This responsibility was moved to the Logger. This is because the Open Tracing API enables the user to specify the log timestamp explicitly:

// OpenTracing.Span
func log(fields: [String: Codable], timestamp: Date)

This is even better for the overall Logging architecture, as now the Logger becomes a "thin facade" for preparing the log's traits before passing them further to the LogFileOutput for doing the "heavy" work.

Testing

Beside unit tests for "create log for Tracing", I also added required integration test. Now the "Send traces for UI Tests" fixture not only sends spans, but also adds log to the "data downloading". Both, spans and logs delivery to HTTPServerMock is asserted in TracingIntegrationTests 🚀.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference

[buranmert]

approved as #120 resolves the discussion here