Cohere Context citations chat engine pack + Jupyter notebook (#11697)

...x-packs/llama-index-packs-cohere-citation-chat/.gitignore

...-index-packs/llama-index-packs-cohere-citation-chat/BUILD

...packs/llama-index-packs-cohere-citation-chat/CHANGELOG.md

...dex-packs/llama-index-packs-cohere-citation-chat/Makefile

...ex-packs/llama-index-packs-cohere-citation-chat/README.md

...cks/llama-index-packs-cohere-citation-chat/examples/BUILD

...citation-chat/examples/cohere_citation_chat_example.ipynb

...lama-index-packs-cohere-citation-chat/examples/example.py

...itation-chat/llama_index/packs/cohere_citation_chat/BUILD

...n-chat/llama_index/packs/cohere_citation_chat/__init__.py

...ation-chat/llama_index/packs/cohere_citation_chat/base.py

...cks/cohere_citation_chat/citations_context_chat_engine.py

...tion-chat/llama_index/packs/cohere_citation_chat/types.py

...tion-chat/llama_index/packs/cohere_citation_chat/utils.py

...cks/llama-index-packs-cohere-citation-chat/pyproject.toml

...-packs/llama-index-packs-cohere-citation-chat/tests/BUILD

.../llama-index-packs-cohere-citation-chat/tests/__init__.py

...re-citation-chat/tests/test_packs_cohere_citation_chat.py