incase sensitive http headers

[barispeker]

Hello,

When receiving B3 propagation http headers they can be lowercase like "x-b3-traceid" but petabridge check this key as case sensitive uppercase . (linkerd can changes these headers to lowercase which http headers are lowercase by default)

 internal const string B3TraceId = "X-B3-TraceId";
 internal const string B3SpanId = "X-B3-SpanId";
 internal const string B3ParentId = "X-B3-ParentSpanId";

......


 public ApplicationInsightsSpanContext Extract(ITextMap carrier)
        {
            string traceId = null;
            string spanId = null;
            string parentId = null;
            foreach (var entry in carrier)
                switch (entry.Key)
                {
                    case B3TraceId:
                        traceId = entry.Value;
                        break;
                    case B3SpanId:
                        spanId = entry.Value;
                        break;
                    case B3ParentId:
                        parentId = entry.Value;
                        break;
                }

            if (traceId != null && spanId != null) // don't care of ParentId is null or not
                return new ApplicationInsightsSpanContext(traceId, spanId, parentId);
            return null;
        }

[Aaronontheweb]

closed via #29