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

[garypretty]

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.

[tomlm]

🕐

[garypretty]

Agreed with @christopheranderson that, providing we go ahead with this approach, we will not obselete the existing telemetry bits until R9 - this will allow us to run the two side by side until all of our messaging etc is up to date and also to provide us with a chance to ensure that the new bits meet the demands of adaptive too.

This also presents the possibility of us deferring the JS and other repo updates to R9 as well if we don't get through them all next week.

[garypretty]

Update: Due to the fact that if we pursue a non-breaking change then 100% of people who have telemetry enabled within their existing bots will need to make changes to migrate to an updated configuration, coupled with the fact that it is very likely that the number of people to extend the IBotTelemetryClient interface within their own solution is incredibly small - the decision has been taken to extend the interface.
This allows us to allow the vast majority of existing telemetry users to gain the new capabilities without making any changes within their solution. It also does not preclude us from replacing the interface in the future.

cc @cleemullins / @scheyal

[garypretty]

Implemented additional interface / extension method to avoid breaking change as discussed with @johnataylor

This is outdated now