Add migration flow

[Dhghomon]

This is the second major change to Easy EdgeDB since the PR a month ago that incorporated changes from Devon's massive onboarding feedback, syntax capitalization and various random other things: #96

That first PR was already long enough so intentionally avoided anything that would have cascading effects like a change in one chapter that changes the schema in the next and then the next.

The PR this time adds migration flow, namely all the necessary changes for a reader to use Easy EdgeDB with the migration tools instead of the manual commands before. Back when I first made Easy EdgeDB the migration tools were rougher and I had a Surface Go (!) so even pasting a migration command led to screens and screens of text and if something didn't match...so a lot of the book had some guesswork in what output would show up at any time.

There are also a number of changes where EdgeDB itself has improved since alpha, like enums and dates being able to be made before the unix epoch (important for this book which is set in the 19th century).

There is a lot of outright rewriting sections too (too many to mention here but check the commits) where the original felt weird, unnecessary or just wrong. And those had their own cascading effects down the chain.

Chinese: I attempted to keep it up to date with the English version but very soon saw just how much there was to change to add the migration flow so mostly gave up. Where possible though I harmonized them with the English version.

To keep the PR relatively small(!) I purposely avoided adding new content on some of the neat features (such as Globals), though some like date_duration snuck in pretty easily. And I couldn't resist the temptation to mention the splat operator in the section on the introspect keyword because the output with the double splat is so fantastic and shows just how much there is to see when you use that keyword. But the remainder will be for later.

After this PR is done there are three (four?) major changes planned.

• Adding interactivity to the questions at the end of each chapter as mentioned here Interactivity #30
• A PR to add new content like globals, grouping, etc. This will probably be combined with a few extra chapters and making those changes will lead to other cascading changes. This will probably be the biggest PR of them all.
• EdgeDB 3.0 new functionality and syntax. Might/Probably will be the first after this PR depending on how hard we want to push people to 3.0. The only hiccup is that 3.0 syntax won't work on someone running on version 2, but then again if someone already has a project on version 2 they are probably already pretty familiar with EdgeDB and it's always a little depressing when you come across a textbook and find out that it isn't using the latest syntax. So I'm leaning towards pushing towards 3.0 sooner rather than later.
• More images and artwork since the original edition only got so far on that.