Remove direct Store calls from the Api layer for the file api4/channe… (#15754)

Co-authored-by: Agniva De Sarker <agnivade@yahoo.co.in>

api4/channel.go

@@ -1736,9 +1736,9 @@ func channelMemberCountsByGroup(c *Context, w http.ResponseWriter, r *http.Reque
 
 	includeTimezones := r.URL.Query().Get("include_timezones") == "true"
 
-	channelMemberCounts, err := c.App.Srv().Store.Channel().GetMemberCountsByGroup(c.Params.ChannelId, includeTimezones)
+	channelMemberCounts, err := c.App.GetMemberCountsByGroup(c.Params.ChannelId, includeTimezones)
 	if err != nil {
-		c.Err = model.NewAppError("Api4.channelMemberCountsByGroup", "app.channel.get_member_count.app_error", nil, err.Error(), http.StatusInternalServerError)
+		c.Err = err
 		return
 	}