GRAILS-10533 - allow customizing the name associated with a collection in the hal json

This allows a custom renderer to be registered with something like this…

// Place your Spring DSL code here
beans = {
    accountCollRenderer(grails.rest.render.hal.HalJsonCollectionRenderer, com.demo.SomeDomainClass) {
        embeddedName = 'mystuff'
    }
}

We need to settle on what the property name should be.  Right now it is "embeddedName" which can probably be improved.