Add 'Data Source' label for the default datasource template variable. (#672)

* Add 'Datasource' label for the default datasource template variable.

Signed-off-by: Tom Wilkie <[email protected]>

* Actually, Data Source is two words.

Signed-off-by: Tom Wilkie <[email protected]>

Author: tomwilkie

grafana-builder/grafana.libsonnet

@@ -92,7 +92,7 @@
             value: datasource,
           },
           hide: 0,
-          label: null,
+          label: 'Data Source',
           name: 'datasource',
           options: [],
           query: 'prometheus',