Storage bandwidth is wasted during template uploads/imports

At the moment when a template is being imported (via url or upload) there is a phase called "Installing template" or something similar. From what I noticed this phase calculates a hash and saves it to the database by reading the downloaded file over the storage network.
During this phase the template is not usable and I believe that should not be the case. I understand that the hash has a purpose and I am not saying it should be removed but I believe this should be an optional task that should be done in background.

In the following examples I do not consider disk speeds, just network speed/bandwidth.
For normal templates this is not necessarily noticeable. Consider this scenario (best case):
Template size: 4GB
Ingress bandwidth: 100 mb/s
Storage bandwidth: 1 gb/s
Download time required: 5.45 seconds
Installing template time required: ~0.6 seconds

Most templates (not ISOs) however are considerably larger, some could be even up to 500 GB (I do have a few templates that I have to import with very large sizes).
In such a case, installing template time required would be about 75 seconds (best case).

During this time (installing template time) the whole bandwidth available for the storage network (if it even is on a separate NIC) would be used up by this process resulting in bad performance for the cluster.

Ways to fix this would be:
1. either compute the hash as the transfer is happening.
2. make it optional (maybe even opt-in) and do it in background only (maybe even limit the bandwidth used for this)

先追蹤「Installing template」階段周圍的模板 URL/上傳匯入路徑，然後找出下載的檔案在哪裡從儲存空間重新讀取，以及其雜湊在哪裡儲存。比較傳輸與從儲存空間讀取的步驟。完成的標準是：模板可用性不會被一次獨立的完整儲存空間讀取所阻塞，同時必要的雜湊仍然正確，且已定義所提議的背景處理或頻寬行為。

由索引模型根據 Issue 內容生成。