RUM-3853 feat(otel-tracer): add test cases for setting active span

[ganeshnj]

What and why?

Some tests to cover active span cases.

How?

There are various a parent can be set

1. Explicit parent

        let span = tracer.spanBuilder(spanName: "parentSpan").setSpanKind(spanKind: .client).startSpan()
        span.setAttribute(key: sampleKey, value: sampleValue)
        let childSpan = tracer.spanBuilder(spanName: "childSpan").setSpanKind(spanKind: .client).setParent(span).startSpan()
        childSpan.setAttribute(key: sampleKey, value: sampleValue)
        childSpan.end()
        span.end()

2. On the context provider

        let span = tracer.spanBuilder(spanName: "parentSpan").setSpanKind(spanKind: .client).startSpan()
        span.setAttribute(key: sampleKey, value: sampleValue)
        OpenTelemetry.instance.contextProvider.setActiveSpan(span)
        let childSpan = tracer.spanBuilder(spanName: "childSpan").setSpanKind(spanKind: .client).startSpan()
        childSpan.setAttribute(key: sampleKey, value: sampleValue)
        childSpan.end()
        span.end()

3. On span builder

        let span = tracer.spanBuilder(spanName: "parentSpan").setSpanKind(spanKind: .client).setActive(true).startSpan()
        span.setAttribute(key: sampleKey, value: sampleValue)
        let childSpan = tracer.spanBuilder(spanName: "childSpan").setSpanKind(spanKind: .client).startSpan()
        childSpan.setAttribute(key: sampleKey, value: sampleValue)
        childSpan.end()
        span.end()

These all have the same impact in the end.

We have all the cases covered and this PR only adds test coverage for them.

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
• Add CHANGELOG entry for user facing changes

Custom CI job configuration (optional)

• Run unit tests for Core, RUM, Trace, Logs, CR and WVT
• Run unit tests for Session Replay
• Run integration tests
• Run smoke tests
• Run tests for tools/

[ncreated]

Looks good 👍, I like how nice the integration test reads 👌