OAI: Add ability to specify fastchat prompt template

Sometimes fastchat may not be able to detect the prompt template from
the model path. Therefore, add the ability to set it in config.yml or
via the request object itself.

Also send the provided prompt template on model info request.

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

model.py

@@ -27,6 +27,7 @@ class ModelContainer:
     draft_cache: Optional[ExLlamaV2Cache] = None
     tokenizer: Optional[ExLlamaV2Tokenizer] = None
     generator: Optional[ExLlamaV2StreamingGenerator] = None
+    prompt_template: Optional[str] = None
 
     cache_fp8: bool = False
     gpu_split_auto: bool = True
@@ -48,6 +49,7 @@ class ModelContainer:
                 'max_seq_len' (int): Override model's default max sequence length (default: 4096)
                 'rope_scale' (float): Set RoPE scaling factor for model (default: 1.0)
                 'rope_alpha' (float): Set RoPE alpha (NTK) factor for model (default: 1.0)
+                'prompt_template' (str): Manually sets the prompt template for this model (default: None)
                 'chunk_size' (int): Sets the maximum chunk size for the model (default: 2048)
                     Inferencing in chunks reduces overall VRAM overhead by processing very long sequences in smaller
                     batches. This limits the size of temporary buffers needed for the hidden state and attention
@@ -93,6 +95,9 @@ class ModelContainer:
             self.config.set_low_mem()
         """
 
+        # Set prompt template override if provided
+        self.prompt_template = kwargs.get("prompt_template")
+
         chunk_size = min(unwrap(kwargs.get("chunk_size"), 2048), self.config.max_seq_len)
         self.config.max_input_len = chunk_size
         self.config.max_attn_size = chunk_size ** 2