IP2P model loading support.

This is the code to load the model and inference it with only a text
prompt. This commit does not contain the nodes to properly use it with an
image input.

This supports both the original SD1 instructpix2pix model and the
diffusers SDXL one.

comfy/supported_models_base.py

@@ -16,6 +16,8 @@ class BASE:
         "num_head_channels": 64,
     }
 
+    required_keys = {}
+
     clip_prefix = []
     clip_vision_prefix = None
     noise_aug_config = None
@@ -28,10 +30,14 @@ class BASE:
     manual_cast_dtype = None
 
     @classmethod
-    def matches(s, unet_config):
+    def matches(s, unet_config, state_dict=None):
         for k in s.unet_config:
             if k not in unet_config or s.unet_config[k] != unet_config[k]:
                 return False
+        if state_dict is not None:
+            for k in s.required_keys:
+                if k not in state_dict:
+                    return False
         return True
 
     def model_type(self, state_dict, prefix=""):