OAI: Add response_prefix and fix BOS token issues in chat completions

response_prefix is used to add a prefix before generating the next
message. This is used in many cases such as continuining a prompt
(see #96).

Also if a template has BOS token specified, add_bos_token will
append two BOS tokens. Add a check which strips a starting BOS token
from the prompt if it exists.

Signed-off-by: kingbri <bdashore3@proton.me>

endpoints/OAI/utils/completion.py

@@ -94,8 +94,8 @@ async def generate_completion(data: CompletionRequest, model_path: pathlib.Path)
 
     try:
         generation = await model.container.generate(data.prompt, **data.to_gen_params())
-
         response = _create_response(generation, model_path.name)
+
         return response
     except Exception as exc:
         error_message = handle_request_error(