Plugins: Refactor creation of plugin context to dedicated service (#66451)

* first pass

* fix tests

* return errs

* change signature

* tidy

* delete unnecessary fields from test

* tidy

* fix tests

* simplify

* separate error check in API

* apply nits

pkg/expr/nodes.go

@@ -16,7 +16,6 @@ import (
 	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/services/datasources"
 	"github.com/grafana/grafana/pkg/services/featuremgmt"
-	"github.com/grafana/grafana/pkg/services/pluginsintegration/adapters"
 )
 
 var (
@@ -207,20 +206,14 @@ func (dn *DSNode) Execute(ctx context.Context, now time.Time, _ mathexp.Vars, s
 	ctx, span := s.tracer.Start(ctx, "SSE.ExecuteDatasourceQuery")
 	defer span.End()
 
-	dsInstanceSettings, err := adapters.ModelToInstanceSettings(dn.datasource, s.decryptSecureJsonDataFn(ctx))
+	pCtx, err := s.pCtxProvider.GetWithDataSource(ctx, dn.datasource.Type, dn.request.User, dn.datasource)
 	if err != nil {
-		return mathexp.Results{}, fmt.Errorf("%v: %w", "failed to convert datasource instance settings", err)
-	}
-	pc := backend.PluginContext{
-		OrgID:                      dn.orgID,
-		DataSourceInstanceSettings: dsInstanceSettings,
-		PluginID:                   dn.datasource.Type,
-		User:                       dn.request.User,
+		return mathexp.Results{}, err
 	}
 	span.SetAttributes("datasource.type", dn.datasource.Type, attribute.Key("datasource.type").String(dn.datasource.Type))
 
 	req := &backend.QueryDataRequest{
-		PluginContext: pc,
+		PluginContext: pCtx,
 		Queries: []backend.DataQuery{
 			{
 				RefID:         dn.refID,