feat: add inpaint mask generation functionality

uses rembg, see https://github.com/danielgatis/rembg

modules/config.py

@@ -318,6 +318,12 @@ example_inpaint_prompts = get_config_item_or_set_default(
 
 example_inpaint_prompts = [[x] for x in example_inpaint_prompts]
 
+default_inpaint_mask_model = get_config_item_or_set_default(
+    key='default_inpaint_mask_model',
+    default_value='isnet-general-use',
+    validator=lambda x: isinstance(x, str)
+)
+
 config_dict["default_loras"] = default_loras = default_loras[:5] + [['None', 1.0] for _ in range(5 - len(default_loras))]
 
 possible_preset_keys = [