Geomap: Add color gradients to route layer (#59062)

* Geomap: Add color gradients to route layer

* Add support for all color schemes

* Address PR feedback: remove ! from verified object

* Add arrow support and simplify color functions

* Simplify and clean-up code

* Remove line width slider and drive width by size

* Drive arrow size based on size

* Allow arrows for fixed color

* Add gdev dashboard

* Use square line caps only when arrows are active

* Apply size to width for fixed color and size

* Handle arrows when size and color are fixed

* Add tags to gdev dashboard

* Fix null error in backend test for gdev dashboard

Co-authored-by: nmarrs <nathanielmarrs@gmail.com>

devenv/jsonnet/dev-dashboards.libsonnet

@@ -205,6 +205,13 @@ local dashboard = grafana.dashboard;
         id: 0,
       }
     },
+    dashboard.new('geomap-route-layer', import '../dev-dashboards/panel-geomap/geomap-route-layer.json') +
+    resource.addMetadata('folder', 'dev-dashboards') +
+    {
+      spec+: {
+        id: 0,
+      }
+    },
     dashboard.new('geomap-spatial-operations-transformer', import '../dev-dashboards/panel-geomap/geomap-spatial-operations-transformer.json') +
     resource.addMetadata('folder', 'dev-dashboards') +
     {