Check for empty URLs when creating/updating a data source (#42837)

* checks for empty URLs added

* check for TimeSeriesTypeNot to fix InfluxDB alerts

* log a warning when a data frame is ignored

* fix: add brittle Prometheus URL input selector

needs a proper aria-label or test-data-id selector

* test: add URL input aria-label

needs to use the grafana/e2e-selectors package

* test: run ci

* add URL validation for specific data sources, e2e tests

* Update pkg/api/datasource/validation.go

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

* delete duplicated logs

* delete unnecessary leading newline

Co-authored-by: gillesdemey <gilles.de.mey@gmail.com>
Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

pkg/tsdb/cloudmonitoring/cloudmonitoring.go

@@ -58,13 +58,13 @@ var (
 )
 
 const (
-	gceAuthentication         string = "gce"
-	jwtAuthentication         string = "jwt"
-	metricQueryType           string = "metrics"
-	sloQueryType              string = "slo"
-	mqlEditorMode             string = "mql"
-	crossSeriesReducerDefault string = "REDUCE_NONE"
-	perSeriesAlignerDefault   string = "ALIGN_MEAN"
+	gceAuthentication         = "gce"
+	jwtAuthentication         = "jwt"
+	metricQueryType           = "metrics"
+	sloQueryType              = "slo"
+	mqlEditorMode             = "mql"
+	crossSeriesReducerDefault = "REDUCE_NONE"
+	perSeriesAlignerDefault   = "ALIGN_MEAN"
 )
 
 func ProvideService(httpClientProvider httpclient.Provider, tracer tracing.Tracer) *Service {