Closes #14312: Move ConfigRevision to core (#14328)

* Move ConfigRevision model & write migrations

* Move ConfigRevision resources from extras to core

* Extend migration to update original content type for ConfigRevision

netbox/core/models/config.py

@@ -0,0 +1,66 @@
+from django.core.cache import cache
+from django.db import models
+from django.urls import reverse
+from django.utils.translation import gettext, gettext_lazy as _
+
+from utilities.querysets import RestrictedQuerySet
+
+__all__ = (
+    'ConfigRevision',
+)
+
+
+class ConfigRevision(models.Model):
+    """
+    An atomic revision of NetBox's configuration.
+    """
+    created = models.DateTimeField(
+        verbose_name=_('created'),
+        auto_now_add=True
+    )
+    comment = models.CharField(
+        verbose_name=_('comment'),
+        max_length=200,
+        blank=True
+    )
+    data = models.JSONField(
+        blank=True,
+        null=True,
+        verbose_name=_('configuration data')
+    )
+
+    objects = RestrictedQuerySet.as_manager()
+
+    class Meta:
+        ordering = ['-created']
+        verbose_name = _('config revision')
+        verbose_name_plural = _('config revisions')
+
+    def __str__(self):
+        if not self.pk:
+            return gettext('Default configuration')
+        if self.is_active:
+            return gettext('Current configuration')
+        return gettext('Config revision #{id}').format(id=self.pk)
+
+    def __getattr__(self, item):
+        if item in self.data:
+            return self.data[item]
+        return super().__getattribute__(item)
+
+    def get_absolute_url(self):
+        if not self.pk:
+            return reverse('core:config')  # Default config view
+        return reverse('core:configrevision', args=[self.pk])
+
+    def activate(self):
+        """
+        Cache the configuration data.
+        """
+        cache.set('config', self.data, None)
+        cache.set('config_version', self.pk, None)
+    activate.alters_data = True
+
+    @property
+    def is_active(self):
+        return cache.get('config_version') == self.pk