feat: Use selected LlamaCloud index in multi-agent template (#350)

.changeset/witty-hotels-do.md

...ates/components/multiagent/python/app/api/routers/chat.py

templates/components/multiagent/python/app/engine/engine.py

...components/multiagent/python/app/examples/choreography.py

...components/multiagent/python/app/examples/orchestrator.py

...s/components/multiagent/python/app/examples/researcher.py

...tes/components/multiagent/python/app/examples/workflow.py

...es/types/streaming/fastapi/app/api/routers/chat_config.py