Mil4n0r/halstack 16 migration

[Mil4n0r]

Checklist (Check off all the items before submitting)

• [ ] Build process is done without errors. All tests pass in the /lib directory.
• [ ] Self-reviewed the code before submitting.
• [ ] Meets accessibility standards.
• [ ] Added/updated documentation to /website as needed.
• [ ] Added/updated tests as needed.

Description Add Migration documentation to the site.

There are still a few TODO elements but the skeleton is more or less ready.

Apart from that, I need to restructure our doc site to allow an additional level of hierarchy for the tokens and migration sections (this requires a refactor of the intermediate structure that we currently use).

OC-19382