Remove `autoAttach`

[ritch]

Details TBD.

This was a failed attempt at allowing models to declare a dependency. As of 2.0 this dependency is more explicit (see PersistedModel). This change will require similarly explicit dependency for Email, Push and similar models.

[bajtos]

Before we can remove autoAttach, we need to implement a mechanism for attaching an existing model to a datasource via models.json without creating a subclass - see loopbackio/loopback-datasource-juggler#119.

[bajtos]

FWIW, loopback-boot 2.0 split the boot in two phases: model definition (models/*.json) and model configuration (models.json). It is possible to configure any model in models.json file as long as it can be found via loopback.getModel(name), which is true for built-in models.

[bajtos]

This can be done in a way that would allow people to use loopback-boot@1.x together with loopback@2.x.

[bajtos]

The current status:

• loopback-boot@1.x comes with it's own implementation of autoAttach, thus the method can be safely dropped from loopback
• as for attaching an existing model to a datasource via models.json, that's already supported in loopback-boot@2.x.

Conclusion: the only remaining blocker is that we need a next major version of loopback.