Prometheus: Fix Azure authentication support (#44407)

Re-adding back Azure authentication support to Prometheus datasource 
after the datasource query logic was rewritten from plugin.json routes to 
Go backend.

Ref #35857

pkg/tsdb/prometheus/prometheus.go

@@ -16,6 +16,7 @@ import (
 	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/infra/tracing"
 	"github.com/grafana/grafana/pkg/tsdb/intervalv2"
+	"github.com/grafana/grafana/pkg/util/maputil"
 	apiv1 "github.com/prometheus/client_golang/api/prometheus/v1"
 )
 
@@ -42,7 +43,7 @@ func ProvideService(httpClientProvider httpclient.Provider, tracer tracing.Trace
 
 func newInstanceSettings(httpClientProvider httpclient.Provider) datasource.InstanceFactoryFunc {
 	return func(settings backend.DataSourceInstanceSettings) (instancemgmt.Instance, error) {
-		var jsonData promclient.JsonData
+		var jsonData map[string]interface{}
 		err := json.Unmarshal(settings.JSONData, &jsonData)
 		if err != nil {
 			return nil, fmt.Errorf("error reading settings: %w", err)
@@ -54,10 +55,15 @@ func newInstanceSettings(httpClientProvider httpclient.Provider) datasource.Inst
 			return nil, err
 		}
 
+		timeInterval, err := maputil.GetStringOptional(jsonData, "timeInterval")
+		if err != nil {
+			return nil, err
+		}
+
 		mdl := DatasourceInfo{
 			ID:           settings.ID,
 			URL:          settings.URL,
-			TimeInterval: jsonData.TimeInterval,
+			TimeInterval: timeInterval,
 			getClient:    pc.GetClient,
 		}