Port of DLAI LlamaIndex Agent short course lessons 2-4 to use Llama 3 (#594)

.github/scripts/spellcheck_conf/wordlist.txt

...uilding_Agentic_RAG_with_Llamaindex_L2_Tool_Calling.ipynb

...with_Llamaindex_L3_Building_an_Agent_Reasoning_Loop.ipynb

..._with_Llamaindex_L4_Building_a_Multi-Document_Agent.ipynb

...pes/3p_integrations/llamaindex/dlai_agentic_rag/README.md