Make mirror feature more configurable (#16957)

Rename`[repository]` `DISABLE_MIRRORS` to `[mirror]` `DISABLE_NEW_PULL`  and add `ENABLED` and `DISABLE_NEW_PUSH` with the below meanings:

- `ENABLED`: **true**: Enables the mirror functionality. Set to **false** to disable all mirrors.
- `DISABLE_NEW_PULL`: **false**: Disable the creation of **new** mirrors. Pre-existing mirrors remain valid.
- `DISABLE_NEW_PUSH`: **false**: Disable the creation of **new** push mirrors. Pre-existing mirrors remain valid.


Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>

services/mirror/mirror.go

@@ -22,6 +22,10 @@ var mirrorQueue = sync.NewUniqueQueue(setting.Repository.MirrorQueueLength)
 
 // Update checks and updates mirror repositories.
 func Update(ctx context.Context) error {
+	if !setting.Mirror.Enabled {
+		log.Warn("Mirror feature disabled, but cron job enabled: skip update")
+		return nil
+	}
 	log.Trace("Doing: Update")
 
 	handler := func(idx int, bean interface{}) error {
@@ -89,15 +93,24 @@ func syncMirrors(ctx context.Context) {
 
 // InitSyncMirrors initializes a go routine to sync the mirrors
 func InitSyncMirrors() {
+	if !setting.Mirror.Enabled {
+		return
+	}
 	go graceful.GetManager().RunWithShutdownContext(syncMirrors)
 }
 
 // StartToMirror adds repoID to mirror queue
 func StartToMirror(repoID int64) {
+	if !setting.Mirror.Enabled {
+		return
+	}
 	go mirrorQueue.Add(fmt.Sprintf("pull %d", repoID))
 }
 
 // AddPushMirrorToQueue adds the push mirror to the queue
 func AddPushMirrorToQueue(mirrorID int64) {
+	if !setting.Mirror.Enabled {
+		return
+	}
 	go mirrorQueue.Add(fmt.Sprintf("push %d", mirrorID))
 }