Telemetry for page views - count and visit time

[shahm5]

Added Azure App Insights logging to keep track of page views and page view times

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• [x] If introducing new functionality or modified behavior, are they backed by unit tests?
• [x] Have all unit tests passed locally? (by running npm run test command)
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[ghost]

All CLA requirements met.

[YingXue]

This does not seem to be right fix for test, as now we have duplicates in app.config and app.*.config. We have two things to do here:

1. I assume that we have verified manually that using app.*.config before this commit does make things functional, the app is choosing the right string respectively
2. Look into how Jest can mock up the config values to get rid of the errors.

No worries on the dups of the reply. All you would need to do is, simply write appConfig.telemetryConnString = 'someteststring' in all the tests where it's saying 'missing instrument key'. That's my understanding, please check if that works, and revert the last change.