fix: return deleted models that have relations

[jaulz]

• Added or updated tests
• Documented user facing changes
• Updated CHANGELOG.md

Changes

Right now, it's not possible to return deleted models and query relations at the same time. For example, when running a mutation that deletes a model I would like to still return the model that was just deleted but if any of its relations is queried as well it will run into an exception, e.g.:

Error: Call to a member function getAttributes() on null in /app/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Collection.php:96
Stack trace:
#0 /app/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Collection.php(119): Illuminate\Database\Eloquent\Collection->loadAggregate(Array, '*', 'count')
#1 /app/vendor/nuwave/lighthouse/src/Execution/ModelsLoader/CountModelsLoader.php(18): Illuminate\Database\Eloquent\Collection->loadCount(Array)
#2 /app/vendor/nuwave/lighthouse/src/Execution/BatchLoader/RelationBatchLoader.php(68): Nuwave\Lighthouse\Execution\ModelsLoader\CountModelsLoader->load(Object(Illuminate\Database\Eloquent\Collection))
#3 /app/vendor/nuwave/lighthouse/src/Execution/BatchLoader/RelationBatchLoader.php(49): Nuwave\Lighthouse\Execution\BatchLoader\RelationBatchLoader->resolve()
#4 /app/vendor/webonyx/graphql-php/src/Executor/Promise/Adapter/SyncPromise.php(63): Nuwave\Lighthouse\Execution\BatchLoader\RelationBatchLoader->Nuwave\Lighthouse\Execution\BatchLoader\{closure}()

This PR serves as a draft and is open to discussion how to handle for example the following cases:

• Shall we return null or 0 on related counts?
• Shall we return null or empty array on related collections?

Breaking changes

tbd

[spawnia]

I would like to still return the model that was just deleted

Why though? I am starting to doubt if Lighthouse should do that.