Prometheus: Add support to make parallel queries (#90316)

* Add support for prometheus datasource to make parallel queries

* Incorporate review comments

* Update pkg/promlib/querydata/request.go

Co-authored-by: ismail simsek <ismailsimsek09@gmail.com>

* Fix lint

* Add parallel queries behind feature flag

* Fixing lint issue

* Update go.mod

* Update pkg/promlib/querydata/request.go

* Update pkg/promlib/querydata/request.go

---------

Co-authored-by: ismail simsek <ismailsimsek09@gmail.com>
Co-authored-by: Charandas <542168+charandas@users.noreply.github.com>

pkg/services/featuremgmt/toggles_gen.json

@@ -2183,6 +2183,18 @@
         "frontend": true
       }
     },
+    {
+      "metadata": {
+        "name": "prometheusRunQueriesInParallel",
+        "resourceVersion": "1720677541862",
+        "creationTimestamp": "2024-07-11T05:59:01Z"
+      },
+      "spec": {
+        "description": "Enables running Prometheus queries in parallel",
+        "stage": "privatePreview",
+        "codeowner": "@grafana/observability-metrics"
+      }
+    },
     {
       "metadata": {
         "name": "publicDashboards",