[AzureWeAppCounters] Set specific sdkVersion for the Azure WebApps counters telemetry item

[SergeyKanzhelev]

When creating and reporting counters from azure webapp - set specific sdkVersion so we will have indication on how counter was collected

[SergeyKanzhelev]

This one is easy:

1. Create static internal variable like this with the VersionPrefix equal to azwapc:

  var sdkVersion = SdkVersionUtils.VersionPrefix + SdkVersionUtils.GetAssemblyVersion();

1. In all gauges set sdkVersion in MetricTelemetry here like this:

   metric.Context.GetInternalContext().SdkVersion = sdkVersion;

2. Verify that you see proper sdkVersion in received metircs

[SergeyKanzhelev]

Committed in https://github.com/Microsoft/ApplicationInsights-SDK-Labs/pull/55