SessionGroup for multi-agent & MCP

[k82cn]

Motivation

Currently, Flame will create a session when chatting with Agent. If there're multi-agents or MCP tool call, it's hard to group the sessions for debug, analysis and so on. In this feature, we'd like to introduce SessionGroup to manage a banch of session, e.g. security, data, analysis and so on.

Function Specification

1. Introduce SessionGroup in Flame
2. Each session should belong to a group; if none, the default group will be used
3. The scheduler should also be enhanced to share resource cross groups

Additional context

None

[k82cn]

Move to roadmap for now. For security, we're going to use User/OAuth2 to handle that; for analysis, let's use labels for that.