[Doc] Implement developer guides for the new WebUI

[carma12]

In order to guide new contributors to the new WebUI, it is necessary to have developer guides that explain and document some aspects of the application (debugging, testing, implementation of new features, navigation, etc.).

E.g.: Similar to what is done in the current WebUI: https://github.com/freeipa/freeipa/tree/master/install/ui/doc/guides

This requires a good understanding of the project, identifying the key components and patterns needed in the implementation/testing/other aspects, and writing how-to guides providing the context needed.