Request to allow eager load for old_value and new_value

[jrbecart]

I have a page that display all the changes made by a user.
For this use case I added the following enhancement to speed up considerably my revision page.

I created a model extending \Venturecraft\Revisionable\Revision and added some relation like:

public function old_relation_a()
{
    return $this->belongsTo('App\Models\Relation_a','old_value');
}

public function new_relation_a()
{
    return $this->belongsTo('App\Models\Relation_a','new_value');
}

And in GetValue function from \Venturecraft\Revisionable\Revision.php I added this:

+ $item = ($this->relations[$which . "_" . $related_model] ?? null);
                    
+ if(!$item)
+ {
  $related_class = $main_model->$related_model()->getRelated();

  // Finally, now that we know the namespace of the related model
  // we can load it, to find the information we so desire
  $item = $related_class::find($this->$which_value);
+ }

Finally I load my revisions like this:

// Example 
$res = \App\Models\MyRevision::where('user_id', $user->id)->get();
$res->where('revisionable_type', 'App\Models\User')->load('user'); // eager load user model
$res->where('key', 'user_type_id')->load('old_user_type'); // eager load related model (like old_relation_a)
$res->where('key', 'user_type_id')->load('new_user_type'); // eager load related model (like new_relation_a)

This way I can speed up my load page and decrease considerably the number of queries.
I will be great to add it, let me know if you want this and I can create a PR.
(I actually have this change in my model, but I have to reuse most of the parent method)