GRPC TraceContext Tags overwrite warnings

[mathewc]

Seeing lots of warnings coming from this code, indicating that we're often overwriting trace context values.

This doesn't seem right. We should investigate to see why this happens and if it should be a Warning.

FunctionsLogs
| where PreciseTimeStamp > ago(1d)
| where Level == 3
| where Summary contains "writing"
| where Source startswith "Worker.LanguageWorkerChannel."
| where Summary startswith "Overwriting"
| project PreciseTimeStamp, Level, Summary
| take 10

[jviau]

Saw this for a couple node apps today. It looks like we are for some reason mapping the entire log scope back into Activity.Tags. Here is where we do it: https://github.com/Azure/azure-webjobs-sdk/blob/dev/src/Microsoft.Azure.WebJobs.Logging.ApplicationInsights/ApplicationInsightsLogger.cs#L412

The big question is, why do we do this? It doesn't seem right. This is actually causing significant log churn when it is hit, leading to noticeable perf impact.