Added new java server tutorial (#6386)

* Added new java server tutorial

* Update courses/free-courses-en.md

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

Co-authored-by: Jonathan Chang <jonathanchang@Jonathans-MacBook-Air.local>
Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

courses/free-courses-en.md

@@ -463,6 +463,7 @@
 * [Java Programming](https://testautomationu.applitools.com/java-programming-course/) - Angie Jones (Applitools)
 * [Java Programming](https://java-programming.mooc.fi) - University of Helsinki
 * [Java Programming: Solving Problems with Software](https://www.coursera.org/learn/java-programming) - (Coursera)
+* [Java Server Tutorials - Happy Coding](https://happycoding.io/tutorials/java-server/) - Kevin Workman
 * [Java tutorial for beginners](https://youtube.com/playlist?list=PLZPZq0r_RZOMhCAyywfnYLlrjiVOkdAI1) - Bro Code (YouTube)
 * [Java Tutorial for Complete Beginners](https://www.udemy.com/course/java-tutorial/) - John Purcell (Udemy)
 * [Learn how to program: Java](https://www.learnhowtoprogram.com/java-june-2017) - Epicodus Inc.