Alerting: fix bug where user is able to access rules from namespaces user is not part of (#41403) (#41406)

* Add fix
* Add tests
(cherry picked from commit 6220872633)

Co-authored-by: Yuriy Tseretyan <yuriy.tseretyan@grafana.com>
Co-authored-by: Armand Grillet <2117580+armandgrillet@users.noreply.github.com>
Co-authored-by: Jean-Philippe Quéméner <JohnnyQQQQ@users.noreply.github.com>
Co-authored-by: George Robinson <george.robinson@grafana.com>
Co-authored-by: gotjosh <josue@grafana.com>

pkg/tests/api/alerting/api_prometheus_test.go

@@ -761,6 +761,32 @@ func TestPrometheusRulesPermissions(t *testing.T) {
 			"evaluationTime": 0
 		}]
 	}
+}`, string(b))
+	}
+
+	// remove permissions from _ALL_ folders
+	require.NoError(t, store.UpdateDashboardACL(1, nil))
+
+	// make sure that no folders are included in the response
+	{
+		promRulesURL := fmt.Sprintf("http://grafana:password@%s/api/prometheus/grafana/api/v1/rules", grafanaListedAddr)
+		// nolint:gosec
+		resp, err := http.Get(promRulesURL)
+		require.NoError(t, err)
+		t.Cleanup(func() {
+			err := resp.Body.Close()
+			require.NoError(t, err)
+		})
+		b, err := ioutil.ReadAll(resp.Body)
+		require.NoError(t, err)
+		require.Equal(t, 200, resp.StatusCode)
+
+		require.JSONEq(t, `
+{
+	"status": "success",
+	"data": {
+		"groups": []
+	}
 }`, string(b))
 	}
 }