docs: new magento 2 cli docs

[skirianov]

Docs changes to align with the new CLI process

Description

Restructured docs.

Joined both installation steps on the same page.

Removed Magento configuration as it's not required to be on a separate page anymore.

Edited Vue Storefront configuration to be only an advanced configuration.

Related Issue

Motivation and Context

With the new CLI tool, old docs are not suitable anymore.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [-] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[mattmaribojoc]

Really great work, left some comments where things were confusing for me - probably because I don't have domain knowledge of Magento, so feel free to ignore if you think more context isn't needed.