Call Cohere RAG inference with `documents` argument (#13196)

...core/llama_index/core/prompts/default_prompt_selectors.py

...ama-index-llms-cohere/llama_index/llms/cohere/__init__.py

...s/llama-index-llms-cohere/llama_index/llms/cohere/base.py

.../llama-index-llms-cohere/llama_index/llms/cohere/utils.py

...ns/llms/llama-index-llms-cohere/tests/test_llms_cohere.py

.../llms/llama-index-llms-cohere/tests/test_rag_inference.py