Mirror System Notice reports are too frequent (#12438)

This PR switches off the success reports from the Update Mirrors cron job
as they are too frequent and not necessarily helpful.

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

modules/cron/setting.go

@@ -17,13 +17,15 @@ type Config interface {
 	DoRunAtStart() bool
 	GetSchedule() string
 	FormatMessage(name, status string, doer *models.User, args ...interface{}) string
+	DoNoticeOnSuccess() bool
 }
 
 // BaseConfig represents the basic config for a Cron task
 type BaseConfig struct {
-	Enabled    bool
-	RunAtStart bool
-	Schedule   string
+	Enabled         bool
+	RunAtStart      bool
+	Schedule        string
+	NoSuccessNotice bool
 }
 
 // OlderThanConfig represents a cron task with OlderThan setting
@@ -53,6 +55,11 @@ func (b *BaseConfig) DoRunAtStart() bool {
 	return b.RunAtStart
 }
 
+// DoNoticeOnSuccess returns whether a success notice should be posted
+func (b *BaseConfig) DoNoticeOnSuccess() bool {
+	return !b.NoSuccessNotice
+}
+
 // FormatMessage returns a message for the task
 func (b *BaseConfig) FormatMessage(name, status string, doer *models.User, args ...interface{}) string {
 	realArgs := make([]interface{}, 0, len(args)+2)