Plugins: Transform plugin support (#20036)

currently temporary separate http api

pkg/api/api.go

@@ -328,6 +328,7 @@ func (hs *HTTPServer) registerRoutes() {
 		// metrics
 		apiRoute.Post("/tsdb/query", bind(dtos.MetricRequest{}), Wrap(hs.QueryMetrics))
 		apiRoute.Post("/tsdb/query/v2", bind(dtos.MetricRequest{}), Wrap(hs.QueryMetricsV2))
+		apiRoute.Post("/tsdb/transform", bind(dtos.MetricRequest{}), Wrap(hs.Transform))
 		apiRoute.Get("/tsdb/testdata/scenarios", Wrap(GetTestDataScenarios))
 		apiRoute.Get("/tsdb/testdata/gensql", reqGrafanaAdmin, Wrap(GenerateSQLTestData))
 		apiRoute.Get("/tsdb/testdata/random-walk", Wrap(GetTestDataRandomWalk))