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/ml/model.go

@@ -0,0 +1,83 @@
+package ml
+
+import (
+	"strings"
+	"time"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	jsoniter "github.com/json-iterator/go"
+)
+
+type CommandConfiguration struct {
+	Type       string              `json:"type"`
+	IntervalMs *uint               `json:"intervalMs,omitempty"`
+	Config     jsoniter.RawMessage `json:"config"`
+}
+
+type OutlierCommandConfiguration struct {
+	DatasourceType string `json:"datasource_type"`
+	DatasourceUID  string `json:"datasource_uid,omitempty"`
+
+	// If Query is empty it should be contained in a datasource specific format
+	// inside of QueryParms.
+	Query       string                 `json:"query,omitempty"`
+	QueryParams map[string]interface{} `json:"query_params,omitempty"`
+
+	Algorithm    map[string]interface{} `json:"algorithm"`
+	ResponseType string                 `json:"response_type"`
+}
+
+// outlierAttributes is outlier command configuration that is sent to Machine learning API
+type outlierAttributes struct {
+	OutlierCommandConfiguration
+	GrafanaURL         string               `json:"grafana_url"`
+	StartEndAttributes timeRangeAndInterval `json:"start_end_attributes"`
+}
+
+type outlierData struct {
+	Attributes outlierAttributes `json:"attributes"`
+}
+
+// outlierRequestBody describes a request body that is sent to Outlier API
+type outlierRequestBody struct {
+	Data outlierData `json:"data"`
+}
+
+type timeRangeAndInterval struct {
+	Start    mlTime `json:"start"`
+	End      mlTime `json:"end"`
+	Interval int64  `json:"interval"` // Interval is expected to be in milliseconds
+}
+
+func newTimeRangeAndInterval(from, to time.Time, interval time.Duration) timeRangeAndInterval {
+	return timeRangeAndInterval{
+		Start:    mlTime(from),
+		End:      mlTime(to),
+		Interval: interval.Milliseconds(),
+	}
+}
+
+// mlTime is a time.Time that is marshalled as a string in a format is  supported by Machine Learning API
+type mlTime time.Time
+
+func (t *mlTime) UnmarshalJSON(b []byte) error {
+	s := strings.Trim(string(b), "\"")
+	parsed, err := time.Parse(timeFormat, s)
+	if err != nil {
+		return err
+	}
+	*t = mlTime(parsed)
+	return nil
+}
+
+// MarshalJSON implements the Marshaler interface.
+func (t mlTime) MarshalJSON() ([]byte, error) {
+	return []byte("\"" + time.Time(t).Format(timeFormat) + "\""), nil
+}
+
+// outlierResponse is a model that represents a response of the outlier proxy API.
+type outlierResponse struct {
+	Status string                     `json:"status"`
+	Data   *backend.QueryDataResponse `json:"data,omitempty"`
+	Error  string                     `json:"error,omitempty"`
+}