added Stable Diffusion 3 support alongside ComfyUI configuration

this commit adds four environment variables:

- COMFYUI_CFG_SCALE
- COMFYUI_SAMPLER
- COMFYUI_SCHEDULER
- COMFYUI_SD3 (merely setting this at all will enable SD3 mode)

backend/apps/images/utils/comfyui.py

@@ -190,7 +190,10 @@ class ImageGenerationPayload(BaseModel):
     width: int
     height: int
     n: int = 1
-
+    cfg_scale: Optional[float] = None
+    sampler: Optional[str] = None
+    scheduler: Optional[str] = None
+    sd3: Optional[bool] = None
 
 def comfyui_generate_image(
     model: str, payload: ImageGenerationPayload, client_id, base_url
@@ -199,6 +202,18 @@ def comfyui_generate_image(
 
     comfyui_prompt = json.loads(COMFYUI_DEFAULT_PROMPT)
 
+    if payload.cfg_scale:
+        comfyui_prompt["3"]["inputs"]["cfg"] = payload.cfg_scale
+
+    if payload.sampler:
+        comfyui_prompt["3"]["inputs"]["sampler"] = payload.sampler
+
+    if payload.scheduler:
+        comfyui_prompt["3"]["inputs"]["scheduler"] = payload.scheduler
+
+    if payload.sd3:
+        comfyui_prompt["5"]["class_type"] = "EmptySD3LatentImage"
+
     comfyui_prompt["4"]["inputs"]["ckpt_name"] = model
     comfyui_prompt["5"]["inputs"]["batch_size"] = payload.n
     comfyui_prompt["5"]["inputs"]["width"] = payload.width