Manual Image name doesn't support architecture

[lizable]

Describe the bug A clear and concise description of what the bug is. 문제가 발생하는 상황에 대한 요약 설명을 적어주세요. When creating a session via "manual image name", It fallbacks to x86_64(AMD64) without any explicit notice and there's no way to set the architecture on user demand, which degrades the user experience.

To Reproduce Steps to reproduce the behavior: 문제를 재현하기 위한 순서를 자세히 적어주세요:

⚠️ NOTE: You may need to execute the agent component in a non x86_64 architecture machine(e.g. any machines with Apple Silicon(aarch64), etc.) since the fallback architecture of image is x86_64.

1. Set debug or allowManualImageNameForSession in config file to true
2. Go to 'Sessions' or 'Summary' page.
3. Click 'Start' button.
4. Session launcher dialog pops up.
5. Input cr.backend.ai/multiarch/python:3.9-ubuntu20.04 in manual image name field.
6. Click Confirm and Launch button at the bottom of the dialog without any input in the manual image name field.
7. See the error. (the session you just created will show "no available instance."

Expected behavior A clear and concise description of what you expected to happen. 원래 기대했던 동작은 어떤 것인지 명확하게 적어주세요. There are two things to make clear about this issue.

• [ ] Although The fallback(or default) architecture is x86_64, we should explicitly display it.
• [ ] Provide user interface(probably select UI) for selecting architecture (if user wants)

Screenshots If applicable, add screenshots to help explain your problem. Just take a screenshot in your clipboard or copy a picture file and paste it here (Ctrl+V/Cmd+V) so that GitHub automatically attach and insert it. 가능하다면, 문제 상황을 보여주는 스크린샷을 첨부해주세요. 클립보드에 스크린샷을 찍거나 이미지 파일을 복사해서 여기에 붙여넣으면(Ctrl+V/Cmd+V) GitHub이 자동으로 이곳에 첨부 및 삽입해줍니다.

Client:

• OS: [e.g. macOS 10.14, Windows 10 (1903)]
• App version: [e.g. 19.08.3] (if you are using a GUI client app)
• Browser version: [e.g. Chrome 76, Safari, Edge] (if you are using a GUI web console)
• Python version: [e.g. 3.7.4] (if you are using the Python SDK)
• NodeJS version: [e.g. 12.0] (if you are using the Javascript SDK)

Server:

• OS: [e.g. Ubuntu 18.04, CentOS 7.6, macOS 10.14]
  • Output of uname -a: [e.g. Linux node01 4.15.0-54-generic #58-Ubuntu SMP Mon Jun 24 10:55:24 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux]
• Backend.AI version: [e.g. 19.09.0]
• Python version: [e.g. 3.6.8]
• Installation method: [e.g. on-premise, using cloud.backend.ai service, used scripts/install-dev.sh]

Additional context Add any other context about the problem here. 추가적으로 문제 상황을 설명할 수 있는 다른 맥락을 기술해주세요. Also, we've been applying "architecture" as an extra argument in CreateIfNotExists(..., architecture) function JS SDK from 22.03, but for better compatibility with former versions(21.09, 21.03), It's better to be treated inside the argument that already exists.