Update App Insights logic and instrumentation key in layout

[JoeProgrammer88]

Summary

Changed Application Insights enablement to require only the connection string, not the instrumentation key. Updated the JavaScript instrumentation key to use our new modern Application Insights resource instead of the classic one

Copilot Summary

This pull request makes two small but important changes to the Application Insights configuration in the _Layout.cshtml file. It simplifies the logic for enabling Application Insights and updates the instrumentation key used in the configuration.

• Application Insights configuration updates:
  • Simplified the logic for enabling Application Insights by removing the check for the old ApplicationInsights:InstrumentationKey and only checking for APPLICATIONINSIGHTS_CONNECTION_STRING.
  • Updated the hardcoded instrumentationKey value in the Application Insights configuration to a new key.