[docs/update-grafana-dashboard-docs] Update Grafana dashboard instructions

Instructions to add Grafana dashboard do not work. The proposed
functions are wrong, according to
[grafana.libsonnet](https://github.com/brancz/kubernetes-grafana/blob/master/grafana/grafana.libsonnet)
`dashboards` and `rawDashboards` should be used in `grafana+::`
field.

This PR updates the existing documentation and fixes minor typos.

docs/developing-prometheus-rules-and-grafana-dashboards.md

@@ -312,7 +312,7 @@ local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {
 { ['grafana-' + name]: kp.grafana[name] for name in std.objectFields(kp.grafana) }
 ```
 
-Incase you have lots of json dashboard exported out from grafan UI the above approch is going to take lots of time. to improve performance we can use `rawGrafanaDashboards` field and provide it's value as json string by using importstr
+In case you have lots of json dashboard exported out from grafana UI the above approach is going to take lots of time to improve performance we can use `rawDashboards` field and provide it's value as json string by using `importstr`
 [embedmd]:# (../examples/grafana-additional-rendered-dashboard-example-2.jsonnet)
 ```jsonnet
 local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {

examples/grafana-additional-jsonnet-dashboard-example.jsonnet

@@ -9,7 +9,8 @@ local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {
   _config+:: {
     namespace: 'monitoring',
   },
-  grafanaDashboards+:: {
+  grafana+:: {
+    dashboards+:: {
       'my-dashboard.json':
         dashboard.new('My Dashboard')
         .addTemplate(
@@ -34,6 +35,7 @@ local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {
                     .addTarget(prometheus.target('vector(1)')))
         ),
     },
+  },
 };
 
 { ['00namespace-' + name]: kp.kubePrometheus[name] for name in std.objectFields(kp.kubePrometheus) } +

examples/grafana-additional-rendered-dashboard-example-2.jsonnet

@@ -2,9 +2,11 @@ local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {
   _config+:: {
     namespace: 'monitoring',
   },
-  rawGrafanaDashboards+:: {
+  grafana+:: {
+    rawDashboards+:: {
       'my-dashboard.json': (importstr 'example-grafana-dashboard.json'),
     },
+  },
 };
 
 { ['00namespace-' + name]: kp.kubePrometheus[name] for name in std.objectFields(kp.kubePrometheus) } +

examples/grafana-additional-rendered-dashboard-example.jsonnet

@@ -2,9 +2,14 @@ local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {
   _config+:: {
     namespace: 'monitoring',
   },
-  grafanaDashboards+:: {
+  grafanaDashboards+:: { //  monitoring-mixin compatibility
     'my-dashboard.json': (import 'example-grafana-dashboard.json'),
   },
+  grafana+:: {
+    dashboards+:: { // use this method to import your dashboards to Grafana
+      'my-dashboard.json': (import 'example-grafana-dashboard.json'),
+    },
+  },
 };
 
 { ['00namespace-' + name]: kp.kubePrometheus[name] for name in std.objectFields(kp.kubePrometheus) } +