Reduce usage of db.DefaultContext (#27073)

Part of #27065

This reduces the usage of `db.DefaultContext`. I think I've got enough
files for the first PR. When this is merged, I will continue working on
this.

Considering how many files this PR affect, I hope it won't take to long
to merge, so I don't end up in the merge conflict hell.

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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/admin/admin.go

@@ -182,7 +182,7 @@ func CronTasks(ctx *context.Context) {
 func MonitorStats(ctx *context.Context) {
 	ctx.Data["Title"] = ctx.Tr("admin.monitor.stats")
 	ctx.Data["PageIsAdminMonitorStats"] = true
-	bs, err := json.Marshal(activities_model.GetStatistic().Counter)
+	bs, err := json.Marshal(activities_model.GetStatistic(ctx).Counter)
 	if err != nil {
 		ctx.ServerError("MonitorStats", err)
 		return