Provide selecting agent on session creation in limited situation

[lizable]

Is your feature request related to a problem? Please describe. A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] 기능 요청이 특정 문제에 연관된 것이라면 여기에 그 문제를 설명해주세요.

Although manager component has been already providing scheduling algorithms when there are multiple agents in a single resource-group, It would be great to provide the user interface for selecting available agents in session launcher on user demand.

Describe the solution you'd like A clear and concise description of what you want to happen. 어떤 기능이 있으면 좋겠는지 자세히 설명해주세요.

⚠️ NOTE: This feature is available in certain situations below

• The user can access a resource group with multiple agent nodes
• There should be a toggle option for enabling/disabling this feature.

• [ ] Provide selective UI for resource group and associated agents
• [ ] (Optional) Show available resource for each agent in resource group

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered. 혹시 다른 대안들을 생각해본 적이 있다면 함께 적어주세요.

Additional context Add any other context or screenshots about the feature request here. 기능 요청에 대해 보다 잘 이해할 수 있는 다른 맥락을 기술해주세요.

There's another client-side interface that already provides session creation with selected agent node. Please refer to the code below: https://github.com/lablup/backend.ai/blob/dcb9bb5f8250a9733d6c68930df62bb4610f0a7a/src/ai/backend/client/cli/session.py#L118-L121