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/models/datasource.go

@@ -13,7 +13,15 @@ const (
 	DS_INFLUXDB_08    = "influxdb_08"
 	DS_ES             = "elasticsearch"
 	DS_PROMETHEUS     = "prometheus"
+	DS_ALERTMANAGER   = "alertmanager"
+	DS_JAEGER         = "jaeger"
+	DS_LOKI           = "loki"
+	DS_OPENTSDB       = "opentsdb"
+	DS_TEMPO          = "tempo"
+	DS_ZIPKIN         = "zipkin"
 	DS_MYSQL          = "mysql"
+	DS_POSTGRES       = "postgres"
+	DS_MSSQL          = "mssql"
 	DS_ACCESS_DIRECT  = "direct"
 	DS_ACCESS_PROXY   = "proxy"
 	DS_ES_OPEN_DISTRO = "grafana-es-open-distro-datasource"