Move InitDBEngine from routers to better place

[6543]

gitea/routers/common/db.go

Lines 19 to 39 in 1bfb0a2

	func InitDBEngine(ctx context.Context) (err error) {
	log.Info("Beginning ORM engine initialization.")
	for i := 0; i < setting.Database.DBConnectRetries; i++ {
	select {
	case <-ctx.Done():
	return fmt.Errorf("Aborted due to shutdown:\nin retry ORM engine initialization")
	default:
	}
	log.Info("ORM engine initialization attempt #%d/%d...", i+1, setting.Database.DBConnectRetries)
	if err = models.NewEngine(ctx, migrations.Migrate); err == nil {
	break
	} else if i == setting.Database.DBConnectRetries-1 {
	return err
	}
	log.Error("ORM engine initialization attempt #%d/%d failed. Error: %v", i+1, setting.Database.DBConnectRetries, err)
	log.Info("Backing off for %d seconds", int64(setting.Database.DBConnectBackoff/time.Second))
	time.Sleep(setting.Database.DBConnectBackoff)
	}
	models.HasEngine = true
	return nil
	}

"...I think this might be better in modules/database.

If you think about what else is in here they're all handlers/middleware of some sort - this is very definitely not and therefore should not be here. ..."

Originally posted by @zeripath in #15800 (comment)

[wxiaoguang]

It should have been done.