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/project-static/package.json

@@ -29,9 +29,9 @@
     "color2k": "^2.0.0",
     "dayjs": "^1.11.5",
     "flatpickr": "4.6.13",
+    "gridstack": "^7.2.3",
     "htmx.org": "^1.8.0",
     "just-debounce-it": "^3.1.1",
-    "masonry-layout": "^4.2.2",
     "query-string": "^7.1.1",
     "sass": "^1.55.0",
     "simplebar": "^5.3.9",
@@ -56,4 +56,4 @@
   "resolutions": {
     "@types/bootstrap/**/@popperjs/core": "^2.11.6"
   }
-}
+}