fix: add migration message on startup of v1 Proxy (#2301)

Add migration message to v1 startup.

cmd/cloud_sql_proxy/cloud_sql_proxy.go

@@ -547,6 +547,12 @@ use the value from the flag, Not compatible with -fuse.`,
 		defer cleanup()
 	}
 
+	// Notify users of v2 Proxy and suggest migrating
+	logging.Infof("This is the Cloud SQL Proxy v1. It is no longer receiving " +
+		"active feature development. For the latest features and improvements, " +
+		"migrate to the v2 version of the Cloud SQL Proxy. For details, see: " +
+		"https://github.com/GoogleCloudPlatform/cloud-sql-proxy/blob/main/migration-guide.md")
+
 	if *quiet {
 		logging.Infof("Cloud SQL Auth proxy logging has been disabled by the -quiet flag. All messages (including errors) will be suppressed.")
 		logging.DisableLogging()