10348 add decimal custom field (#10422)

* 10348 add decimal custom field

* 10348 fix tests

* 10348 add documentation

* Rearrange custom fields to be ordered consistently

* Rename number_field to integer_field for clarity

* Clean up validation logic

* Apply suggested changes from PR

* Store decimal custom field values natively

* Fix filter test

* Update custom field model migrations to use new encoder

Co-authored-by: jeremystretch <jstretch@ns1.com>

netbox/utilities/json.py

@@ -0,0 +1,17 @@
+import decimal
+
+from django.core.serializers.json import DjangoJSONEncoder
+
+__all__ = (
+    'CustomFieldJSONEncoder',
+)
+
+
+class CustomFieldJSONEncoder(DjangoJSONEncoder):
+    """
+    Override Django's built-in JSON encoder to save decimal values as JSON numbers.
+    """
+    def default(self, o):
+        if isinstance(o, decimal.Decimal):
+            return float(o)
+        return super().default(o)