Influx: Support flux in the influx datasource (#25308)

* add flux 
* add token to datasource config editor
* add backend for flux
* make the interpolated query available in query inspector
* go mod tidy
* Chore: fixes a couple of strict null errors in influxdb plugin

Co-authored-by: kyle <kyle@grafana.com>
Co-authored-by: Lukas Siatka <lukasz.siatka@grafana.com>

pkg/tsdb/influxdb/flux/executor.go

@@ -0,0 +1,88 @@
+package flux
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	influxdb2 "github.com/influxdata/influxdb-client-go"
+)
+
+// ExecuteQuery runs a flux query using the QueryModel to interpolate the query and the runner to execute it.
+// maxSeries somehow limits the response.
+func ExecuteQuery(ctx context.Context, query QueryModel, runner queryRunner, maxSeries int) (dr backend.DataResponse) {
+	dr = backend.DataResponse{}
+
+	flux, err := Interpolate(query)
+	if err != nil {
+		dr.Error = err
+		return
+	}
+
+	glog.Debug("Flux", "interpolated query", flux)
+
+	tables, err := runner.runQuery(ctx, flux)
+	if err != nil {
+		dr.Error = err
+		return
+	}
+
+	dr = readDataFrames(tables, int(float64(query.MaxDataPoints)*1.5), maxSeries)
+
+	for _, frame := range dr.Frames {
+		if frame.Meta == nil {
+			frame.Meta = &data.FrameMeta{}
+		}
+		frame.Meta.ExecutedQueryString = flux
+	}
+
+	return dr
+}
+
+func readDataFrames(result *influxdb2.QueryTableResult, maxPoints int, maxSeries int) (dr backend.DataResponse) {
+	dr = backend.DataResponse{}
+
+	builder := &FrameBuilder{
+		maxPoints: maxPoints,
+		maxSeries: maxSeries,
+	}
+
+	for result.Next() {
+		// Observe when there is new grouping key producing new table
+		if result.TableChanged() {
+			if builder.frames != nil {
+				for _, frame := range builder.frames {
+					dr.Frames = append(dr.Frames, frame)
+				}
+			}
+			err := builder.Init(result.TableMetadata())
+			if err != nil {
+				dr.Error = err
+				return
+			}
+		}
+
+		if builder.frames == nil {
+			dr.Error = fmt.Errorf("Invalid state")
+			return dr
+		}
+
+		err := builder.Append(result.Record())
+		if err != nil {
+			dr.Error = err
+			break
+		}
+	}
+
+	// Add the inprogress record
+	if builder.frames != nil {
+		for _, frame := range builder.frames {
+			dr.Frames = append(dr.Frames, frame)
+		}
+	}
+
+	// Attach any errors (may be null)
+	dr.Error = result.Err()
+	return dr
+}