Backend Plugins: Plugin configuration using Grafana config (#23451)

Enables adding a section `plugin.<plugin id>` and key/value to
Grafana configuration file which will be converted and sent
as environment variables to the backend plugin.
Also sends some additional environment variables, Grafana
version (GF_VERSION), Grafana edition (GF_EDITION) and 
enterprise license path (GF_ENTERPRISE_LICENSE_PATH).

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

Fixes #21515,

pkg/plugins/dashboards_test.go

@@ -8,22 +8,21 @@ import (
 	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/setting"
 	. "github.com/smartystreets/goconvey/convey"
-	"gopkg.in/ini.v1"
 )
 
 func TestPluginDashboards(t *testing.T) {
 	Convey("When asking plugin dashboard info", t, func() {
-		setting.Raw = ini.Empty()
-		sec, _ := setting.Raw.NewSection("plugin.test-app")
-		_, err := sec.NewKey("path", "testdata/test-app")
-		So(err, ShouldBeNil)
-
 		pm := &PluginManager{
 			Cfg: &setting.Cfg{
 				FeatureToggles: map[string]bool{},
+				PluginSettings: setting.PluginSettings{
+					"test-app": map[string]string{
+						"path": "testdata/test-app",
+					},
+				},
 			},
 		}
-		err = pm.Init()
+		err := pm.Init()
 		So(err, ShouldBeNil)
 
 		bus.AddHandler("test", func(query *models.GetDashboardQuery) error {