Update 21.corebot-app-insights to use ConnectionString

[tracyboehrer]

Per Gary:

We have a customer who were experiencing some dropped events from their bot runtime to Application Insights. After investigation and the MS account team engaging with the App Insights, apparently this can happen if you are using the InstrumentationKey and not the Connection String, which the bot runtime currently does.

The new Adaptive Runtime should be updated to use the Connection String and, in fact, it looks like this is required for new Azure regions https://docs.microsoft.com/en-us/azure/azure-monitor/app/asp-net-troubleshoot-no-data

We will need to consider what, if anything we can do for legacy runtime, or what we do if we migrate a runtime that currently has an InstrumentationKey.

Original issue: microsoft/botbuilder-dotnet#5455

[Fl4v]

Hi @tracyboehrer, kind of a random question. How would the application know the endpoint of the application insight without the connection string? Am I missing something?