Chore: Refactor backend plugin manager/tsdb query data (#34944) (#35172)

Move QueryData method into backend plugin manager which HandleRequest uses to
query data from plugin SDK supported data sources. This allowed us to remove a lot
of code no longer needed.

Ref #21510

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>
(cherry picked from commit b3e9087557)

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

pkg/plugins/backendplugin/manager/manager_test.go

@@ -367,6 +367,7 @@ type testPlugin struct {
 	decommissioned bool
 	backend.CollectMetricsHandlerFunc
 	backend.CheckHealthHandlerFunc
+	backend.QueryDataHandlerFunc
 	backend.CallResourceHandlerFunc
 	mutex sync.RWMutex
 }
@@ -441,6 +442,14 @@ func (tp *testPlugin) CheckHealth(ctx context.Context, req *backend.CheckHealthR
 	return nil, backendplugin.ErrMethodNotImplemented
 }
 
+func (tp *testPlugin) QueryData(ctx context.Context, req *backend.QueryDataRequest) (*backend.QueryDataResponse, error) {
+	if tp.QueryDataHandlerFunc != nil {
+		return tp.QueryDataHandlerFunc(ctx, req)
+	}
+
+	return nil, backendplugin.ErrMethodNotImplemented
+}
+
 func (tp *testPlugin) CallResource(ctx context.Context, req *backend.CallResourceRequest, sender backend.CallResourceResponseSender) error {
 	if tp.CallResourceHandlerFunc != nil {
 		return tp.CallResourceHandlerFunc(ctx, req, sender)