Stackdriver: Exposing stackdriver backend api

pkg/models/datasource.go

@@ -22,6 +22,7 @@ const (
 	DS_MSSQL         = "mssql"
 	DS_ACCESS_DIRECT = "direct"
 	DS_ACCESS_PROXY  = "proxy"
+	DS_STACKDRIVER   = "stackdriver"
 )
 
 var (
@@ -70,6 +71,7 @@ var knownDatasourcePlugins = map[string]bool{
 	DS_POSTGRES:                 true,
 	DS_MYSQL:                    true,
 	DS_MSSQL:                    true,
+	DS_STACKDRIVER:              true,
 	"opennms":                   true,
 	"abhisant-druid-datasource": true,
 	"dalmatinerdb-datasource":   true,