docs: streamline tutorials, add and update how-to guides

[edibotopic]

UDENG-3595

This PR makes several significant changes to the structure and content of the UP4W tutorial and the how-to sections of the docs.

The tutorial has been greatly simplified and shortened to focus on installation, adding a Pro token and verifying Pro attachment. There are now an increased number of short how-to guides that aim to be brief and reliable sets of instructions for specific tasks.

Tabbed interfaces are used when presenting alternate configuration options.

Major changes:

• Decoupling of UP4W and Landscape: installation and automatic Pro-attachment with UP4W does not depend on Landscape. The Getting Started tutorial now only covers the process of installing UP4W, configuring Pro and verifying Pro attachment. The tutorial should now be easier to navigate successfully for a first-time user interested in automatic Pro-attachment of Ubuntu WSL instances. This decoupling is also reflected in the how-to guides, which now treat adding a Pro token and configuring Landscape as independent tasks.
• Simplification of installation how-to guide: the original how-to guide on installation and configuration consisted of several dropdown menus, callout blocks and caveats, making it quite difficult to follow for a task that should be straightforward. It has been simplified, in part by presenting a tabbed interface with the two primary options for installing with Windows registry and installing with the graphical Windows application.
• Extraction of short how-to guides from tutorial content: another reason for the length of the original tutorial was the inclusion of sections relating to backing up instances and uninstalling applications. These have been extracted into self-contained how-to guides as they contain useful information that a user is likely to return to for a variety of reasons in the context of Ubuntu WSL in general. They are referenced in the tutorial but are not fully included to avoid breaking up the flow of the tutorial.
• Updated guidelines on Landscape config: the Landscape integration with UP4W has undergone some changes, particularly with respect to the UI. The documentation now reflects these changes.
• Increased elaboration of Windows registry option: using the Windows registry is an important option for enterprise users. It is now given increased prominence in the documentation with some additional text explaining why it is useful and images for user instruction. The getting started tutorial uses the graphical application for installation but the default tab in the how-to guides is for the Windows registry.

Minor changes:

• UI improvements: use of tabbed interfaces for user choice between Windows app and Windows registry
• Internal references: updated internal Sphinx references for many sections
• Rewording/fixes: minor changes throughout
• Updated images: throughout

UDENG-3595

[jibel]

Very good. I noticed one typo.

[CarlosNihelton]

I like very much the proposed structure, just have few minor items to bring into consideration.

[CarlosNihelton]

Very good!

[jibel]

Looks good to me. Thanks for this update!

[edibotopic]

Thanks both -- I will mark the remaining conversations as "resolved" now.