Authorizer updates, debug exceptions and more improvements

Added

• The authorizer now has separate showRelated() and showRelationship() methods. Previously both these controller actions were authorized via the single showRelationship() method. Adding the new showRelated method means developers can now implement separate authorization logic for these two actions if desired. Our default implementation remains unchanged - both are authorized using the view<RelationshipName> method on the relevant policy.
• The request class now has a isCreatingOrUpdating() helper method to determine whether the request is to create or updated a resource.
• Add stop on first failure to all validators in the resource request class.
• #85 When running an application with debug mode turned on, the default JSON:API error object for an exception will now contain detailed exception information, including the stack trace, in the object's meta member.
• #103 Can now fully customise attribute serialization to JSON using the extractUsing() callback. This receives the model, column name and value. This is useful if the developer needs to control the serialization of a few fields on their schema. However, the recommendation is to use a resource class for complete control over the serialization of a model to a JSON:API resource.

Changed

• Minimum Laravel version is now 8.30. This change was required to use the $stopOnFirstFailure property on Laravel's FormRequest class.
• Schema classes no longer automatically sort their fields by name when iterating over them. This change was made to give the developer full control over the order of fields (particularly as this order affects the order in which fields are listed when serialized to a JSON:API resource). Developers can list fields in name order if that is the preferred order.
• Removed the LaravelJsonApi\Spec\UnexpectedDocumentException which was thrown if there was a failure when decoding request JSON content before parsing it for compliance with the JSON:API specification. A JsonApiException will now be thrown instead.

Fixed

• #101 Ensure controller create action always returns a response that will result in a 201 Created response.
• #102 The attach and detach to-many relationship controller actions now correctly resolve the collection query class using the relation's inverse resource type. Previously they were incorrectly using the primary resource type to resolve the query class.