[Dependency: Guides] - Create "Migrating" section and move content from Guides

[TheLarkInn]

Dependency for #1859

Goal: As a user I would like to be able to easily find (starting from the homepage), how to upgrade to the latest version of webpack.

• Create a new Section called "Migrate", it's creation should be at the same tier as "Guides"
  • The url to access this page should be webpack.js.org/migrate
• Move existing Migrating (v1 => v2/3) Guide and place it inside of new Migrating section under
  • This page's url should be webpack.js.org/migrate/3

[onstash]

How about we add a link "Migration" section in the home page in this "It's that simple" section? Or probably something similar? Please let me know your thoughts on this. @TheLarkInn 😅

[TheLarkInn]

We can link to it from that page certainly, but this is just scoped to creating the section itself, and moving the existing guide to the new section location, and then with the PR that @sokra lands with #1939, then we can move that also into this section.

[EugeneHlushko]

@montogeek can you assign this on me, will implement over this weekend

[EugeneHlushko]

@TheLarkInn pls see PR open for any additions