trace root span incorrectly identified due to instrumentation

[ie-pham]

Consider the following trace:

[
    Span{
        traceId: "39343434",
        spanId: "aaa"
        parentSpanId: "",
        links: [
            link{
                traceId: "39343434"
                spanId: "bbb"
                atributes: {
                    "opentracing.ref_type": "child_of"
                }
            }
        ]
    },
    Span{
        traceId: "39343434",
        spanId: "bbb"
        parentSpanId: "",
        links: []
    },
    Span{
        traceId: "39343434",
       spanId: "ccc"
        parentSpanId: "",
        links: [
            link{
                traceId: "39343434"
                spanId: "aaa"
                atributes: {
                    "opentracing.ref_type": "child_of"
                }
            }
        ]
    }
 
 ]

Currently, Tempo labels any spans with an empty parentSpanId field as the root span. In the above situation, Tempo would label whichever of the three spans is ingested last. Tempo should also check whether there is a link with attribute child of before labeling the span as the root span. The correct root span is bbb as it has no child of links.