Add in more model changes around execution environments

- a new unique name field to EE
- a new configure-Tower-in-Tower setting DEFAULT_EXECUTION_ENVIRONMENT
- an Org-level execution_environment_admin_role
- a default_environment field on Project
- a new Container Registry credential type
- order EEs by reverse of the created timestamp
- a method to resolve which EE to use on jobs

awx/main/models/projects.py

@@ -259,6 +259,15 @@ class Project(UnifiedJobTemplate, ProjectOptions, ResourceMixin, CustomVirtualEn
         app_label = 'main'
         ordering = ('id',)
 
+    default_environment = models.ForeignKey(
+        'ExecutionEnvironment',
+        null=True,
+        blank=True,
+        default=None,
+        on_delete=models.SET_NULL,
+        related_name='+',
+        help_text=_('The default execution environment for jobs run using this project.'),
+    )
     scm_update_on_launch = models.BooleanField(
         default=False,
         help_text=_('Update the project when a job is launched that uses the project.'),