Alerting: use static channel configuration to determinate secure fields (#52527) (#52570)

* Alerting: use static channel configuration to determinate secure fields

* move to channels package

* introduce channel_config package to fix cyclic import

* add missing changes

* compare type to type

(cherry picked from commit ba9c18d9c3)

Co-authored-by: Jean-Philippe Quéméner <JohnnyQQQQ@users.noreply.github.com>

pkg/tests/api/alerting/api_available_channel_test.go

@@ -11,7 +11,8 @@ import (
 
 	"github.com/grafana/grafana/pkg/infra/tracing"
 	"github.com/grafana/grafana/pkg/models"
-	"github.com/grafana/grafana/pkg/services/ngalert/notifier"
+
+	"github.com/grafana/grafana/pkg/services/ngalert/notifier/channels_config"
 	"github.com/grafana/grafana/pkg/tests/testinfra"
 )
 
@@ -47,7 +48,7 @@ func TestAvailableChannels(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, 200, resp.StatusCode)
 
-	expNotifiers := notifier.GetAvailableNotifiers()
+	expNotifiers := channels_config.GetAvailableNotifiers()
 	expJson, err := json.Marshal(expNotifiers)
 	require.NoError(t, err)
 	require.Equal(t, string(expJson), string(b))