Allow CLI add to db and clean-up handling of evaluate args

[pseudotensor]

• Allow CLI add to db
• Test making and adding to db in CLI
• Clean-up handling of evaluate args
• Clean-up other kwargs
• Allow CLI choice of various other vectordb args, like which embedding, top k, etc.
• Add langchain readme to isolate some LangChain examples to avoid bloating main readme

============================================================================================= short test summary info =============================================================================================
FAILED tests/test_manual_test.py::test_chat_context - NotImplementedError: MANUAL TEST FOR NOW
=================================================================== 1 failed, 14 passed, 7 skipped, 1 xpassed, 9 warnings in 353.05s (0:05:53) ====================================================================
(h2ollm) jon@pseudotensor:~/h2o-llm$