Database Migration Management Framework

_From @kjdelisle on July 28, 2017 18:37_

## Scenario
FooCorp wants to deploy version 2.0 of their LoopBack application on their production server, but doing so will require some alteration of the schema in their database. Some of these changes require a more delicate touch that cannot necessarily be performed by the `autoupdate` function.

Currently, FooCorp would have to create their own scripts and execute them to modify their database schema to match their expectations, which may require them to more directly interface with drivers that are used by their chosen LoopBack connector, or using another implementation entirely!

## Proposal

Create a component for use in loopback-next that handles the idea of production-system migration within a LoopBack application as it is upgraded from one release to another.

Originally, I had a design in my mind for how this would work, but I noticed that there are some generic migration tools on npm (https://www.npmjs.com/package/migration), and I was wondering if there was anything additional that we'd want to add to make it easier to do this sort of thing.

Martin Fowler's [Evolutionary Database Design](https://www.martinfowler.com/articles/evodb.html) provides a comprehensive information on this topic, including implementation examples.

Other ORM frameworks have been supporting migrations for quite some time, we can inspire from them.
- [Migrations in Ruby on Rails](https://guides.rubyonrails.org/v3.2/migrations.html)
- [.NET EntityFramework's Code First Migrations](https://docs.microsoft.com/en-us/aspnet/mvc/overview/getting-started/getting-started-with-ef-using-mvc/migrations-and-deployment-with-the-entity-framework-in-an-asp-net-mvc-application)

The proposal names no repository files, tests, or entry points. Start by reviewing the migration package idea and the referenced Evolutionary Database Design and ORM migration examples; done would require an agreed production-migration design and its implementation in loopback-next.

Written by the indexing model from the issue text.