Adapt dashboard schema to validate on some devenv dashboards (#37594)

* Remove null values from JSON

* Specify the color field

* Add note about openness of custom field's struct

* Update schemaVersion

* Specify thresholds

* Add panel id

* Add maxDataPoints and interval

* Add mappings, albeit very under-specified

* Allow empty string for timezone field

This is probably not a good idea - same as allowing nulls.

* Allow false for refresh - otherwise, string

* Make threshold value optional

* Make interval optional

* Fix broken and changed decls in ui models

* Add models.cue for timeseries panel

* Fixups for home dashboard

* Add timeShift, timeFrom

* Abstract out #Target, rejigger comments

public/app/plugins/panel/timeseries/models.cue

@@ -0,0 +1,42 @@
+// Copyright 2021 Grafana Labs
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package grafanaschema
+
+import (
+    ui "github.com/grafana/grafana/cue/ui:grafanaschema"
+)
+
+Family: {
+    lineages: [
+        [
+            {
+                PanelOptions: {
+                    legend: ui.VizLegendOptions
+                    tooltip: ui.VizTooltipOptions
+                }
+                PanelFieldConfig: {
+                    ui.LineConfig
+                    ui.FillConfig
+                    ui.PointsConfig
+                    ui.AxisConfig
+                    drawStyle?:    ui.DrawStyle
+                    gradientMode?: ui.GraphGradientMode
+                    hideFrom?:     ui.HideSeriesConfig
+                }
+            }
+        ]
+    ]
+    migrations: []
+}