MM-43145: channels loader (#19957)

Add channels dataloader

https://mattermost.atlassian.net/browse/MM-43145

```release-note
NONE
```

store/timerlayer/timerlayer.go

@@ -1189,22 +1189,6 @@ func (s *TimerLayerChannelStore) GetForPost(postID string) (*model.Channel, erro
 	return result, err
 }
 
-func (s *TimerLayerChannelStore) GetFromMaster(id string) (*model.Channel, error) {
-	start := timemodule.Now()
-
-	result, err := s.ChannelStore.GetFromMaster(id)
-
-	elapsed := float64(timemodule.Since(start)) / float64(timemodule.Second)
-	if s.Root.Metrics != nil {
-		success := "false"
-		if err == nil {
-			success = "true"
-		}
-		s.Root.Metrics.ObserveStoreMethodDuration("ChannelStore.GetFromMaster", success, elapsed)
-	}
-	return result, err
-}
-
 func (s *TimerLayerChannelStore) GetGuestCount(channelID string, allowFromCache bool) (int64, error) {
 	start := timemodule.Now()
 
@@ -1221,6 +1205,22 @@ func (s *TimerLayerChannelStore) GetGuestCount(channelID string, allowFromCache
 	return result, err
 }
 
+func (s *TimerLayerChannelStore) GetMany(ids []string, allowFromCache bool) (model.ChannelList, error) {
+	start := timemodule.Now()
+
+	result, err := s.ChannelStore.GetMany(ids, allowFromCache)
+
+	elapsed := float64(timemodule.Since(start)) / float64(timemodule.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("ChannelStore.GetMany", success, elapsed)
+	}
+	return result, err
+}
+
 func (s *TimerLayerChannelStore) GetMember(ctx context.Context, channelID string, userID string) (*model.ChannelMember, error) {
 	start := timemodule.Now()