clarify supported parameters better in api server

[Stonelinks]

There's a comment for "ignored or currently unsupported" parameters but I'm pretty sure some of them are supported (for instance, I think logprobs is supported?).

Also when I generate an openapi client off the openapi.json there are errors because of these.

So just delete the things that are unsupported or clarify that they're actually supported / provide more info on the existing support.

[Stonelinks]

Just leaving some notes here for parameters i see in app.py

• model: ignored, but currently marked "optional"... on the one hand could mark "required" to make it explicit in case the server supports multiple llama's at the same time, but also could delete it since its ignored. decision: mark it required for the sake of openai api compatibility
• n, presence_penalty, frequency_penalty, best_of, logit_bias, user: not supported, excluded from the calls into llama. decision: delete it
• logprobs (CreateCompletionRequest only): i think this is actually supported (its in the arguments of LLama.__call__, which is how the completion is invoked). decision: mark as supported
• top_k (CreateChatCompletionRequest only): llama.create_chat_completion definitely has a top_k argument, but its missing from CreateChatCompletionRequest. decision: add it