Closes #13381: Enable plugins to register custom data backends (#14095)

* Initial work on #13381

* Fix backend type display in table column

* Fix data source type choices during bulk edit

* Misc cleanup

* Move backend utils from core app to netbox

* Move backend type validation from serializer to model

netbox/core/data_backends.py

@@ -10,61 +10,24 @@ from django import forms
 from django.conf import settings
 from django.utils.translation import gettext as _
 
-from netbox.registry import registry
-from .choices import DataSourceTypeChoices
+from netbox.data_backends import DataBackend
+from netbox.utils import register_data_backend
 from .exceptions import SyncError
 
 __all__ = (
-    'LocalBackend',
     'GitBackend',
+    'LocalBackend',
     'S3Backend',
 )
 
 logger = logging.getLogger('netbox.data_backends')
 
 
-def register_backend(name):
-    """
-    Decorator for registering a DataBackend class.
-    """
-
-    def _wrapper(cls):
-        registry['data_backends'][name] = cls
-        return cls
-
-    return _wrapper
-
-
-class DataBackend:
-    parameters = {}
-    sensitive_parameters = []
-
-    # Prevent Django's template engine from calling the backend
-    # class when referenced via DataSource.backend_class
-    do_not_call_in_templates = True
-
-    def __init__(self, url, **kwargs):
-        self.url = url
-        self.params = kwargs
-        self.config = self.init_config()
-
-    def init_config(self):
-        """
-        Hook to initialize the instance's configuration.
-        """
-        return
-
-    @property
-    def url_scheme(self):
-        return urlparse(self.url).scheme.lower()
-
-    @contextmanager
-    def fetch(self):
-        raise NotImplemented()
-
-
-@register_backend(DataSourceTypeChoices.LOCAL)
+@register_data_backend()
 class LocalBackend(DataBackend):
+    name = 'local'
+    label = _('Local')
+    is_local = True
 
     @contextmanager
     def fetch(self):
@@ -74,8 +37,10 @@ class LocalBackend(DataBackend):
         yield local_path
 
 
-@register_backend(DataSourceTypeChoices.GIT)
+@register_data_backend()
 class GitBackend(DataBackend):
+    name = 'git'
+    label = 'Git'
     parameters = {
         'username': forms.CharField(
             required=False,
@@ -144,8 +109,10 @@ class GitBackend(DataBackend):
         local_path.cleanup()
 
 
-@register_backend(DataSourceTypeChoices.AMAZON_S3)
+@register_data_backend()
 class S3Backend(DataBackend):
+    name = 'amazon-s3'
+    label = 'Amazon S3'
     parameters = {
         'aws_access_key_id': forms.CharField(
             label=_('AWS access key ID'),