Create reference document comparing old/new migration methods

[RaymondFallon]

Many PMACS applications will likely move from using the pmacs-rails_sql_views gem to (scenic + this gem). Can we create a document that compares the old migration methods to the new ones exposed by this gem?

Specifically, developers may wish to upgrade their old migration files when upgrading to this gem. Can we give examples of old pmacs-rails_sql_views migrations and new scenic migrations which would produce identical views?

Two corollaries:

1. Should such a document live in the gem or should we keep that on the PMACS wiki?
2. Should we link to this document in our 5.1 -> 5.2 Rails upgrade notes.

[barendt]

We should definitely create a document to help migrate migrations from the old gem to the new one.

1. I think the document can stick to just the mechanics of the pmacs-rails_sql_views -> scenic transition, so I think it should live in this gem. The other stuff that lives in a migration for one of our apps (CEAL, etc) is all stuff that's separate from the view code and should hopefully not need to be explicitly spelled out in documentation for our developers.
2. We should definitely link to this document, once it's created, in the 5.1 -> 5.2 upgrade notes.

I'm going to create a pointer in GitLab to this issue so that somebody can pick it up during a hackathon, but you should feel free to claim it, @RaymondFallon, if you're interested.