SSE: Support for ML query node (#69963)

* introduce a new node-type ML and implement a command outlier that uses ML plugin as a source of data.
* add feature flag mlExpressions that guards the feature

pkg/expr/testing.go

@@ -0,0 +1,84 @@
+package expr
+
+import (
+	"context"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+
+	"github.com/grafana/grafana/pkg/services/datasources"
+	"github.com/grafana/grafana/pkg/services/user"
+)
+
+type fakePluginContextProvider struct {
+	recordings []struct {
+		method string
+		params []interface{}
+	}
+	result      map[string]*backend.AppInstanceSettings
+	errorResult error
+}
+
+var _ pluginContextProvider = &fakePluginContextProvider{}
+
+func (f *fakePluginContextProvider) Get(_ context.Context, pluginID string, user *user.SignedInUser, orgID int64) (backend.PluginContext, error) {
+	f.recordings = append(f.recordings, struct {
+		method string
+		params []interface{}
+	}{method: "Get", params: []interface{}{pluginID, user, orgID}})
+	if f.errorResult != nil {
+		return backend.PluginContext{}, f.errorResult
+	}
+	var u *backend.User
+	if user != nil {
+		u = &backend.User{
+			Login: user.Login,
+			Name:  user.Name,
+			Email: user.Email,
+		}
+	}
+	return backend.PluginContext{
+		OrgID:                      orgID,
+		PluginID:                   pluginID,
+		User:                       u,
+		AppInstanceSettings:        f.result[pluginID],
+		DataSourceInstanceSettings: nil,
+	}, nil
+}
+
+func (f *fakePluginContextProvider) GetWithDataSource(ctx context.Context, pluginID string, user *user.SignedInUser, ds *datasources.DataSource) (backend.PluginContext, error) {
+	f.recordings = append(f.recordings, struct {
+		method string
+		params []interface{}
+	}{method: "GetWithDataSource", params: []interface{}{pluginID, user, ds}})
+
+	if f.errorResult != nil {
+		return backend.PluginContext{}, f.errorResult
+	}
+
+	orgId := int64(1)
+	if user != nil {
+		orgId = user.OrgID
+	}
+	r, err := f.Get(ctx, pluginID, user, orgId)
+	if ds != nil {
+		r.DataSourceInstanceSettings = &backend.DataSourceInstanceSettings{
+			ID:   ds.ID,
+			UID:  ds.UID,
+			Type: ds.Type,
+			Name: ds.Name,
+		}
+	}
+	return r, err
+}
+
+type recordingCallResourceHandler struct {
+	recordings []*backend.CallResourceRequest
+	response   *backend.CallResourceResponse
+}
+
+var _ backend.CallResourceHandler = &recordingCallResourceHandler{}
+
+func (f *recordingCallResourceHandler) CallResource(_ context.Context, req *backend.CallResourceRequest, sender backend.CallResourceResponseSender) error {
+	f.recordings = append(f.recordings, req)
+	return sender.Send(f.response)
+}