Expressions: use datasource model from the query (#41376)

* refactor datasource loading

* refactor datasource loading

* pass uid

* use dscache in alerting to get DS

* remove expr/translate pacakge

* remove dup injection entry

* fix DS type on metrics endpoint, remove SQL DS lookup inside SSE

* update test and adapter

* comment fix

* Make eval run as admin when getting datasource info

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

* fmt and comment

* remove unncessary/redundant code

Co-authored-by: Kyle Brandt <kyle@grafana.com>
Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: Santiago <santiagohernandez.1997@gmail.com>

pkg/plugins/adapters/adapters.go

@@ -2,6 +2,8 @@
 package adapters
 
 import (
+	"encoding/json"
+
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
 	"github.com/grafana/grafana/pkg/models"
 )
@@ -9,9 +11,13 @@ import (
 // ModelToInstanceSettings converts a models.DataSource to a backend.DataSourceInstanceSettings.
 func ModelToInstanceSettings(ds *models.DataSource, decryptFn func(map[string][]byte) map[string]string,
 ) (*backend.DataSourceInstanceSettings, error) {
-	jsonDataBytes, err := ds.JsonData.MarshalJSON()
-	if err != nil {
-		return nil, err
+	var jsonDataBytes json.RawMessage
+	if ds.JsonData != nil {
+		var err error
+		jsonDataBytes, err = ds.JsonData.MarshalJSON()
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	return &backend.DataSourceInstanceSettings{