Issue a warning from launch script when app will run as root

See gh-10275

spring-boot-project/spring-boot-tools/spring-boot-loader-tools/src/main/resources/org/springframework/boot/loader/tools/launch.script

@@ -128,6 +128,9 @@ log_file="$LOG_FOLDER/$LOG_FILENAME"
 # shellcheck disable=SC2012
 [[ $(id -u) == "0" ]] && run_user=$(ls -ld "$jarfile" | awk '{print $3}')
 
+# Issue an warning if the application will run as root
+[[ $(id -u ${run_user}) == "0" ]] && { echoYellow "Application is running as root (UID 0). This is considered insecure."; }
+
 # Find Java
 if [[ -n "$JAVA_HOME" ]] && [[ -x "$JAVA_HOME/bin/java" ]]; then
     javaexe="$JAVA_HOME/bin/java"