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/extras/dashboard/utils.py

@@ -0,0 +1,76 @@
+import uuid
+
+from django.core.exceptions import ObjectDoesNotExist
+
+from netbox.registry import registry
+from extras.constants import DEFAULT_DASHBOARD
+
+__all__ = (
+    'get_dashboard',
+    'get_default_dashboard',
+    'get_widget_class',
+    'register_widget',
+)
+
+
+def register_widget(cls):
+    """
+    Decorator for registering a DashboardWidget class.
+    """
+    app_label = cls.__module__.split('.', maxsplit=1)[0]
+    label = f'{app_label}.{cls.__name__}'
+    registry['widgets'][label] = cls
+
+    return cls
+
+
+def get_widget_class(name):
+    """
+    Return a registered DashboardWidget class identified by its name.
+    """
+    try:
+        return registry['widgets'][name]
+    except KeyError:
+        raise ValueError(f"Unregistered widget class: {name}")
+
+
+def get_dashboard(user):
+    """
+    Return the Dashboard for a given User if one exists, or generate a default dashboard.
+    """
+    if user.is_anonymous:
+        dashboard = get_default_dashboard()
+    else:
+        try:
+            dashboard = user.dashboard
+        except ObjectDoesNotExist:
+            # Create a dashboard for this user
+            dashboard = get_default_dashboard()
+            dashboard.user = user
+            dashboard.save()
+
+    return dashboard
+
+
+def get_default_dashboard():
+    from extras.models import Dashboard
+    dashboard = Dashboard(
+        layout=[],
+        config={}
+    )
+    for widget in DEFAULT_DASHBOARD:
+        id = str(uuid.uuid4())
+        dashboard.layout.append({
+            'id': id,
+            'w': widget['width'],
+            'h': widget['height'],
+            'x': widget.get('x'),
+            'y': widget.get('y'),
+        })
+        dashboard.config[id] = {
+            'class': widget['widget'],
+            'title': widget.get('title'),
+            'config': widget.get('config', {}),
+        }
+
+    return dashboard