Add mistral instruct chat format as "mistral-instruct" (#799)

* Added mistral instruct chat format as "mistral"

* Fix stop sequence (merge issue)

* Update chat format name to `mistral-instruct`

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Co-authored-by: Andrei <abetlen@gmail.com>

llama_cpp/llama_chat_format.py

@@ -877,6 +877,22 @@ def format_chatml(
     return ChatFormatterResponse(prompt=_prompt, stop=_sep)
 
 
+@register_chat_format("mistral-instruct")
+def format_mistral(
+    messages: List[llama_types.ChatCompletionRequestMessage],
+    **kwargs: Any,
+) -> ChatFormatterResponse:
+    _roles = dict(user="[INST] ", assistant="[/INST]")
+    _sep = " "
+    system_template = """<s>{system_message}"""
+    system_message = _get_system_message(messages)
+    system_message = system_template.format(system_message=system_message)
+    _messages = _map_roles(messages, _roles)
+    _messages.append((_roles["assistant"], None))
+    _prompt = _format_no_colon_single(system_message, _messages, _sep)
+    return ChatFormatterResponse(prompt=_prompt)
+
+
 @register_chat_format("chatglm3")
 def format_chatglm3(
     messages: List[llama_types.ChatCompletionRequestMessage],