Restructure and many fixes.

[rkratky]

What does this PR do?

Restructures the Che 7 docs based on received feedback to reflect:

Overview
    Introduction to Eclipse Che
        Introductory videos
        Features and benefits
    Che quick-starts
        Running Che locally
        Running Che remotely
        Navigating Che using the Dashboard
        Using the IDE
    Hosted Che
    Che architecture

......

End-User Guide
    Che-Theia IDE basics
        Navigating the Che-Theia user interface
        Files and projects
        Editing code and code assistance
        Key bindings
        Searching
        Commands
        Debugging
        Testing
        Version control
        Integrated terminal
        Languages
        SSH
    Using developer workspaces
        Workspaces overview
        Configuring a workspace using a devfile
        Making a workspace portable using a devfile
        Converting a Che 6 Workspace to a Che 7 devfile
        Using and customizing a workspace template - stack
        Exporting a workspace with a Che factory
        Sharing access to a Che workspace
        Remotely accessing Che workspaces
        Creating a workspace from code sample
        Creating a workspace by importing source code of a project
        Importing a Kubernetes application into a Che workspace
        Configuring VCS credentials for workspaces
        Use an alternative Che workspace editor
    Extending Che
        What is a Che-Theia plug-in
        Configuring Che-Theia plug-ins
        Using alternative IDEs in Che
        Using a Visual Studio Code extension in Che
    Troubleshooting for Che end users

......

Installation Guide
    Che installation overview
        Target platforms
        Deployment architecture diagram
    Che installation prerequisites
        Storage
        Networking
        Identity
    Installing Che on different Kubernetes distributions
    Updating Che
    Advanced configuration options
        Che configuration reference table
        Deploying Che with HTTPS mode
        Deploying Che without Keycloak
        Configuring Che Persistent Volumes strategy
        Configuring Che with and without Keycloak
        Configuring private Docker registries
        Configuring email notifications
        Configuring namespace strategies
        Configuring workspace memory settings
        Configuring Che with OpenShift OAuth
    Troubleshooting Che installation

......

Administration Guide
    Removing user data
    Retrieving Che logs
    Customizing devfile registry
    Customizing plug-in registry
    Monitoring Che
    Tracing Che
    Securing Che
    Troubleshooting for Che administrators

......

Contributor Guide
    Developing Che-Theia plug-ins
    Testing Che-Theia plug-ins
    Publishing Che-Theia plug-ins
    Packaging a Visual Studio Code plug-in for Che
    Adding support for a new language
    Adding support for a new debugger
    Che extensibility reference
    API reference

......

Tips and tricks for Che

Che FAQ

Note: "Extending Che" to be fixed based on disc. outcome.

[slemeur]

One comment in:

Overview
...
    Che quick-starts
        Running Che locally
        Running Che remotely

Discussing with @benoitf this morning and we thought it makes more sense to split by target environments:

Overview
...
    Che quick-starts
        Running Che locally
        Running Che on AWS
        Running Che on GCP
        Running Che on Azure

[rkratky]

Che quick-starts

Yes, there'll be separate pages for AWS, GCP, and Azure.

Thanks.