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/forms.py

@@ -0,0 +1,38 @@
+from django import forms
+from django.urls import reverse_lazy
+
+from netbox.registry import registry
+from utilities.forms import BootstrapMixin, add_blank_choice
+from utilities.choices import ButtonColorChoices
+
+__all__ = (
+    'DashboardWidgetAddForm',
+    'DashboardWidgetForm',
+)
+
+
+def get_widget_choices():
+    return registry['widgets'].items()
+
+
+class DashboardWidgetForm(BootstrapMixin, forms.Form):
+    title = forms.CharField(
+        required=False
+    )
+    color = forms.ChoiceField(
+        choices=add_blank_choice(ButtonColorChoices),
+        required=False,
+    )
+
+
+class DashboardWidgetAddForm(DashboardWidgetForm):
+    widget_class = forms.ChoiceField(
+        choices=get_widget_choices,
+        widget=forms.Select(
+            attrs={
+                'hx-get': reverse_lazy('extras:dashboardwidget_add'),
+                'hx-target': '#widget_add_form',
+            }
+        )
+    )
+    field_order = ('widget_class', 'title', 'color')