NGAlerting: Use identity.Requester interface instead of SignedInUser (#76360)

* unfurl SignedInUserAttrs services

* replace signedInUser with Requester

replace signedInUser with requester

* fix tests

* linting

---------

Co-authored-by: Ieva <ieva.vasiljeva@grafana.com>

pkg/services/pluginsintegration/clientmiddleware/user_header_middleware.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
 	"github.com/grafana/grafana/pkg/plugins"
+	"github.com/grafana/grafana/pkg/services/auth/identity"
 	"github.com/grafana/grafana/pkg/services/contexthandler"
 	"github.com/grafana/grafana/pkg/util/proxyutil"
 )
@@ -31,8 +32,9 @@ func (m *UserHeaderMiddleware) applyUserHeader(ctx context.Context, h backend.Fo
 	}
 
 	h.DeleteHTTPHeader(proxyutil.UserHeaderName)
-	if !reqCtx.IsAnonymous {
-		h.SetHTTPHeader(proxyutil.UserHeaderName, reqCtx.Login)
+	namespace, _ := reqCtx.SignedInUser.GetNamespacedID()
+	if namespace != identity.NamespaceAnonymous {
+		h.SetHTTPHeader(proxyutil.UserHeaderName, reqCtx.SignedInUser.GetLogin())
 	}
 }