Add cron running API (#12421)

* Add cron running API

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Apply suggestions from code review

* placate-swagger

Signed-off-by: Andrew Thornton <art27@cantab.net>

* return not found

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Apply suggestions from code review

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

routers/api/v1/swagger/cron.go

@@ -0,0 +1,16 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package swagger
+
+import (
+	api "code.gitea.io/gitea/modules/structs"
+)
+
+// CronList
+// swagger:response CronList
+type swaggerResponseCronList struct {
+	// in:body
+	Body []api.Cron `json:"body"`
+}