feat: support external custom models (#13429)

Co-authored-by: qiuxuan.lzw <qiuxuan.lzw@alibaba-inc.com>
Co-authored-by: Mick <mickjagger19@icloud.com>

test/srt/external_models/custom_qwen2_vl.py

@@ -0,0 +1,21 @@
+from sglang.srt.models.qwen2_vl import (
+    Qwen2VLForConditionalGeneration as OriginalQwen2VLForConditionalGeneration,
+)
+from sglang.srt.multimodal.processors.qwen_vl import QwenVLImageProcessor
+
+
+class Qwen2VLForConditionalGeneration(OriginalQwen2VLForConditionalGeneration):
+    def __init__(self, config, quant_config, prefix: str = "") -> None:
+        super().__init__(config, quant_config, prefix)
+        print("init custom model:", self.__class__.__name__)
+
+
+class CustomProcessor(QwenVLImageProcessor):
+    models = [Qwen2VLForConditionalGeneration]
+
+    def __init__(self, hf_config, server_args, _processor, *args, **kwargs):
+        super().__init__(hf_config, server_args, _processor, *args, **kwargs)
+        print("init custom processor:", self.__class__.__name__)
+
+
+EntryClass = Qwen2VLForConditionalGeneration