Display a message about sampling at start-up (#3700)

Author: jeanbisutti

agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/configuration/ConfigurationBuilder.java

@@ -301,6 +301,8 @@ private static void overlayConfiguration(
     // only fall back to default sampling configuration after all overlays have been performed
     if (config.sampling.requestsPerSecond == null && config.sampling.percentage == null) {
       config.sampling.requestsPerSecond = 5.0;
+      configurationLogger.info(
+          "Some telemetry may be sampled out because a default sampling configuration was added in version 3.4.0 to reduce the default billing cost. You can set the sampling configuration explicitly: https://learn.microsoft.com/azure/azure-monitor/app/java-standalone-config#sampling");
     }
     // only set role instance to host name as a last resort
     if (config.role.instance == null) {

agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/configuration/ConfigurationLogger.java

@@ -17,6 +17,10 @@ void warn(String message, Object... args) {
     messages.add(new Message(ConfigurationLogLevel.WARN, message, args));
   }
 
+  public void info(String message, Object... args) {
+    messages.add(new Message(ConfigurationLogLevel.INFO, message, args));
+  }
+
   void debug(String message, Object... args) {
     messages.add(new Message(ConfigurationLogLevel.DEBUG, message, args));
   }
@@ -50,6 +54,12 @@ public void log(Logger logger, String message, Object... args) {
         logger.warn(message, args);
       }
     },
+    INFO {
+      @Override
+      public void log(Logger logger, String message, Object... args) {
+        logger.info(message, args);
+      }
+    },
     DEBUG {
       @Override
       public void log(Logger logger, String message, Object... args) {