docs: update roadnmap v2.5 and v2.6

[gaius-qi]

Description

This pull request updates the project roadmap documentation for versions 2.5 and 2.6, primarily by moving several planned features from the 2.5 release to 2.6 and adding new enhancements for cluster deployment flexibility and client performance. The changes clarify the release schedule for key features and refine the focus of each release.

Key roadmap adjustments:

Features moved from 2.5 to 2.6:

• The following features were removed from the v2.5 roadmap and re-added or expanded in the v2.6 roadmap:
  • RDMA-based distribution of model weights/files and cache task memory-level download tasks, now under the Client section for v2.6. [1] [2]
  • gRPC Auth Token authentication mechanism, removed from v2.5 Security section (not present in v2.6).

New and expanded v2.6 features:

• Added an option to remove the Manager dependency, allowing clusters to be deployed with just Scheduler and Client, reducing minimum deployment requirements.
• Client improvements:
  • Implementation of a bandwidth-aware negotiation protocol to distribute requests across multiple parent nodes, preventing bottlenecks.
  • RDMA-based file distribution and memory-level cache task downloads now explicitly listed under Client.

Other roadmap clarifications:

• The AI Model/Dataset Distribution section in v2.6 is streamlined, with exploration of SGLang and vLLM ecosystem integration removed.

Related Issue

Motivation and Context