Model: Add vision loading support

Adds the ability to load vision parts of text + image models. Requires
an explicit flag in config because there isn't a way to automatically
determine whether the vision tower should be used.

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

config_sample.yml

@@ -124,6 +124,9 @@ model:
   # NOTE: Only works with chat completion message lists!
   prompt_template:
 
+  # Enables vision support if the model supports it. (default: False)
+  vision: false
+
   # Number of experts to use per token.
   # Fetched from the model's config.json if empty.
   # NOTE: For MoE models only.