update react-java-mysql sample

[glours]

• Be sure the backend create a connection to the database
• Check Mysql version (latest one is 8.0.19)
• Don't use default docker compose network, create a specific one
• Rewrite the react app and be sure to call the backend

[glours]

@jdrouet can you take a look for the react app rewriting 🙏 ?

[jdrouet]

Done and PR ready for review ;)

[glours]

Fix by #13 & #24