[feat] update reactjs sample guide to use dhi example

[kristiyan-velkov]

Description

This PR adds a DHI-based Dockerfile example demonstrating how to build an React.js application using the dhi-node image and serve it through the dhi-nginx image.

Reviews

• [x] Technical review

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[kristiyan-velkov]

Hey, your guide still says the old method to use Docker Harden Images. Please update according to the new method.

Resolved :) Thank you!