Handle related resource URLs

[tobyzerner]

As per https://jsonapi.org/format/#fetching-resources:

The following request fetches an article’s author:

GET /articles/1/author HTTP/1.1
Accept: application/vnd.api+json

These URLs can be implemented automatically as part of the Show endpoint.

For ToOne relationships, we simply get the value of the relationship and show it.

For ToMany relationships, will need to add a queryRelated($model, $field) method to the resource. We then pass this query into the relationship's collection and make filters, pagination etc available.

[faustbrian]

@tobyzerner how far out do you think this is? I'm currently evaluating this package for a new project and this would be the main feature missing currently.

[tobyzerner]

I'm going to need this in one of my own projects soon, so I reckon I might set some time to work on it before January.