Prometheus: Fix passing of custom params when running queries (#42728)

* Prometheus: Fix passing of custom params

* Remove prints

pkg/tsdb/prometheus/custom_query_params_middleware.go

@@ -11,14 +11,25 @@ import (
 const (
 	customQueryParametersMiddlewareName = "prom-custom-query-parameters"
 	customQueryParametersKey            = "customQueryParameters"
+	grafanaDataKey                      = "grafanaData"
 )
 
 func customQueryParametersMiddleware(logger log.Logger) sdkhttpclient.Middleware {
 	return sdkhttpclient.NamedMiddlewareFunc(customQueryParametersMiddlewareName, func(opts sdkhttpclient.Options, next http.RoundTripper) http.RoundTripper {
-		customQueryParamsVal, exists := opts.CustomOptions[customQueryParametersKey]
+		grafanaData, exists := opts.CustomOptions[grafanaDataKey]
 		if !exists {
 			return next
 		}
+
+		data, ok := grafanaData.(map[string]interface{})
+		if !ok {
+			return next
+		}
+		customQueryParamsVal, exists := data[customQueryParametersKey]
+		if !exists {
+			return next
+		}
+
 		customQueryParams, ok := customQueryParamsVal.(string)
 		if !ok || customQueryParams == "" {
 			return next