[PORT] Update TelemetryClient to enable tracking of dialog ('page') views

[tomlm]

Port this change from botbuilder-dotnet/master branch:
microsoft/botbuilder-dotnet#3440

Addresses #3441

Update TelemetryClient to enable tracking of page views and add automatic page view logging on dialog start for component / waterfall dialogs.

This PR now adds a new abstract class, LogTelemetryClient, as well as an implementation of it within the ApplicationInsights library, AppInsightsTelemetryClient. All current consumers of the existing BotTelemetryClient have been updated to use the new client, but leaving the existing functionality in place (marked as obselete) for backwards compatibility.

Changed projects

• Microsoft.Bot.Builder.ApplicationInsights
• Microsoft.Bot.Builder.Dialogs
• Microsoft.Bot.Builder
• integration
• Microsoft.Bot.Builder.ApplicationInsights.Tests
• Microsoft.Bot.Builder.Dialogs.Tests