Update Entando App Builder doc as per changes in 7.5

As per Myriam's suggestion, I will include a paragraph about the new feature in Chapter 1.

Something like this:
Red Hat Process Automation Manager includes a rich, open-source user experience platform for building modern, process-driven applications in the cloud. Business experts can quickly compose applications by dragging and dropping reusable UI components to pages, while Developers are free to work in the frontend frameworks of their choice. A library of out-of-the-box, Micro-Frontend widgets are available; enabling task lists, forms, process graphs and more. The UX platform streamlines development and allows business users to create compelling experiences for customers across a wide range of devices and channels. AppBuilder 6 takes advantage of the cloud native infrastructure provided by Openshift leveraging services like ingress, sidecar and pipelines.