Decide which arguments should be set using defaults

[rwood-97]

Currently, we don't set defaults for many of our arguments in run.py to allow users to set them using env variables. We should go through and decide which ones we want to be this way and which should just be defaults. Potentially for consistency all should be able to be set using environment variables.

[rwood-97]

Maybe we could have:

   parser.add_argument(
        "--mode",
        type=str,
        help=(
            "Select which mode to use "
            "(ignored if not using llama-index-llama-cpp or llama-index-hf). "
            "Default is 'chat'."
        ),
        default=os.environ.get("LLAMA_MODE") or "chat",
        choices=["chat", "query"],

Behaviour:

• If set by flag, use that value
• If not set by flag, but os.environ.get() is not None, use the env variable
• If neither, use the default "chat".

[rchan26]

this is a nice idea - will try!