Support llama-index@^0.11.11 for multi-agent template (#305)

.changeset/good-news-sneeze.md

templates/types/multiagent/fastapi/app/agents/multi.py

templates/types/multiagent/fastapi/app/agents/planner.py

templates/types/multiagent/fastapi/app/api/routers/chat.py

templates/types/multiagent/fastapi/app/examples/workflow.py

templates/types/multiagent/fastapi/pyproject.toml