dove: service.options with scoped adapter-options

[fratzinger]

Where I came from:
I wanted to add the json schema to the service, so I would have add it to the service.options.
I use sql and knex.js and started typing new Service({ ... and saw that it had schema available. I 💯 would have mistaken it to be the json schema.
The knex.js adapter uses three options: Model, name and schema.
While Model is somehow clear, what does the other two even mean? To answer that, I had to take a look in the docs.

What I'm suggesting:
Use adapter-specific options within the adapter key: service.options.knex. So it becomes:

new Service({
  id: 'id',
  multi: ...,
  knex: {
    Model: ...,
    name: ..., // or better: 'tableName'
    schema: ...
  }
});

This has several advantages:

1. Kognitive: you know which options are bound to knex.js or any other adapter
2. You can easily filter services: services.filter(service => !!service.options.knex)
3. schema is free for the json schema.
4. It's the same convention for context.params.knex

I know that would be a breaking change. At least I wanted to open a discussion about it, though.