Multi-Role Cluster Configuration in Session Launcher

We need to redesign the Session Launcher UI to support complex allocation scenarios involving multiple cluster roles. The current design assumes a single accelerator type per session and uniform resource specifications across roles. However, upcoming requirements include:

- **Role-Based Resource Customization**
Allow users to define multiple roles (e.g., main, sub, prefill, decode) within a cluster and configure distinct resource specifications and container images for each role.
- **Dynamic Role Management**
Enable adding or removing roles dynamically, beyond the fixed main/sub structure.
- **Cluster Role vs Cluster Size**
Clarify that cluster size does not equal the number of roles. Each role may have different resource allocations.
- **UI Simplification with Flexibility**
Maintain a simplified default UI for common cases while supporting advanced scenarios like disaggregated serving and heterogeneous accelerators.

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### **Acceptance Criteria**

- Users can add/remove roles in the Session Launcher.
- Each role supports independent resource and image selection.
- UI reflects role-based configuration clearly and intuitively.
- Backend supports dynamic resource slot recognition and allocation.
- Documentation updated to reflect new workflow.

### UX Ideas

- [Joongi Kim: \| project > General | Microsoft Teams|https://teams.microsoft.com/l/message/19:69df14f11f93480caec8975a5326d301@thread.skype/1762395678626?tenantId=13c6a44d-9b52-4b9e-aa34-0513ee7131f2&groupId=483daa8a-29ee-4085-9f71-e93d7f112730&parentMessageId=1727236545420&teamName=project&channelName=General&createdTime=1762395678626]
- [https://lablup.sharepoint.com/:p:/s/devops/ETW9TLNSya5KuwV8bCSYK3YBwqQj8uaPFFq2XuRc4kTiMQ?e=4S94Xn](https://lablup.sharepoint.com/:p:/s/devops/ETW9TLNSya5KuwV8bCSYK3YBwqQj8uaPFFq2XuRc4kTiMQ?e=4S94Xn)

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JIRA Issue: FR-1654