Closes #9416: Dashboard widgets (#11823)

* Replace masonry with gridstack

* Initial work on dashboard widgets

* Implement function to save dashboard layout

* Define a default dashboard

* Clean up widgets

* Implement widget configuration views & forms

* Permit merging dict value with existing dict in user config

* Add widget deletion view

* Enable HTMX for widget configuration

* Implement view to add dashboard widgets

* ObjectCountsWidget: Identify models by app_label & name

* Add color customization to dashboard widgets

* Introduce Dashboard model to store user dashboard layout & config

* Clean up utility functions

* Remove hard-coded API URL

* Use fixed grid cell height

* Add modal close button

* Clean up dashboard views

* Rebuild JS

netbox/users/models.py

@@ -140,7 +140,10 @@ class UserConfig(models.Model):
         # Set a key based on the last item in the path. Raise TypeError if attempting to overwrite a non-leaf node.
         key = keys[-1]
         if key in d and type(d[key]) is dict:
-            raise TypeError(f"Key '{path}' has child keys; cannot assign a value")
+            if type(value) is dict:
+                d[key].update(value)
+            else:
+                raise TypeError(f"Key '{path}' is a dictionary; cannot assign a non-dictionary value")
         else:
             d[key] = value