Document UI Architecture

[joshuawilson]

Child of epic/experience #2498

Description

As a developer of the system, I want be able to easily find, read, and understand the UI architecture.

Acceptance Criteria

• The doc should be easy to find.
• The doc should cover how fabric8-ui is built with the build pipelines (fabric8cd and ci-centos)
• The doc should include information about our platform UI service bus (context, space, logged in user) and design for putting this in a state management system (NGRX).
• The doc should include information about our environmental variables and how to access them from within the platform.
• The doc should include information about how to set environmental variables in the build.

[joshuawilson]

Added https://github.com/fabric8-ui/fabric8-ui/wiki/UI-Architecture-Guide