Feature/custom fields default values (#5389)

* Fixes CustomFieldsetsController::fields() which I think is not used anywhere else and don't think ever worked as you can't call get() on a Collection.
Have tested extensively and doesn't seem to affect anywhere else?

* Adds default value functionality

* Adds built assets

* Fixes assignment to asset_model_id which should have been evaluation and alters route so it sits more in line with existing work

* Updates built assets

* Remove silly docker.env file; fix Dockerfile to preserve Oauth keys (#5377)

* Added department to custom asset export
Updates build assets

* Adds translation support for 'add default values' checkbox label

app/Models/AssetModel.php

@@ -98,6 +98,11 @@ class AssetModel extends SnipeModel
         return $this->belongsTo('\App\Models\CustomFieldset', 'fieldset_id');
     }
 
+    public function defaultValues()
+    {
+        return $this->belongsToMany('\App\Models\CustomField', 'models_custom_fields')->withPivot('default_value');
+    }
+
 
     public function getImageUrl() {
         if ($this->image) {