Microsoft changed the recommended way of configuring Application Insights from using Instrumentation Keys to Connection Strings. As per my conversation with @wicksipedia, we should update this.
### Tasks
- [x] Update the code that loads the connection string
- [x] Update environment variables from `APPINSIGHTS_INSTRUMENTATIONKEY` to `APPINSIGHTS_CONNECTIONSTRING`
- [x] Update GitHub environment variables
cc: @wicksipedia @adamcogan
Microsoft changed the recommended way of configuring Application Insights from using Instrumentation Keys to Connection Strings. As per my conversation with @wicksipedia, we should update this.