Add documentation for Telemetry Logging (#3738)

* Add documentation for TelemetryLogging

Adding the documentation Isao provided in OSS repo, so we have it in a common place

* Update TelemetryLogging.md

docs/TelemetryLogging.md

@@ -0,0 +1,19 @@
+# Enabling telemetry logging with Application Insights 
+
+FHIR server enables telemetry logging to your Application Insights resource by updating the Telemetry section in appsettings.json.  
+1. Application Insights logging package with the Application Insights instrumentation key. 
+1. Application Insights logging package with the Application Insights connection string. 
+
+Properties in Telemetry section in appsettings.json
+* Provider : Telemetry provider is “ApplicationInsights” or “None” for disabling telemetry logging. 
+* InstrumentationKey : The instrumentation key of your Application Insights resource. 
+* ConnectionString : The connection string of your Application Insights resource. 
+
+**Note**: 
+1. Technical support for instrumentation key-based logging in Application Insights will end in March 2025. 
+2. When the instrumentation key and connection string are provided in appsettings.json for ApplicationInsights provider, the instrumentation key will be used. 
+
+Next Steps: OpenTelemetry provider is still experimental-mode, not recommended for production use. 
+To use OTEL, set the provider value to “OpenTelemetry” in appsettings.json. Incase the connection string is used for OpenTelemetry provider, the instrumentation key will be ignored. 
+
+