Rename Dojo 2 migration guide

[dylans]

Both the tutorials and reference guide have content referring to getting ready to migrate to Dojo 2. These should be reworked to explain that this is just to make things modern, as Dojo 2 is quite different than expected at the time those were authored.

[spaceone]

I just wanted to create the same Issue.
Please rename: https://dojotoolkit.org/reference-guide/1.10/releasenotes/migration-2.0.html
Because it only describes migration to Dojo 1.7 and not to Dojo 2.0.

[dylans]

@spaceone I've updated it in the source code for the website (as you've seen), but we're having serious issues rebuilding the old reference guide content on the website.