Feat: supports MinerU http-client/server method (#10961)

### What problem does this PR solve?

Add support for MinerU http-client/server method.

To use MinerU with vLLM server:

1. Set up a vLLM server running MinerU:
   ```bash
   mineru-vllm-server --port 30000
   ```

2. Configure the following environment variables:
- `MINERU_EXECUTABLE=/ragflow/uv_tools/.venv/bin/mineru` (or the path to
your MinerU executable)
   - `MINERU_BACKEND="vlm-http-client"`
   - `MINERU_SERVER_URL="http://your-vllm-server-ip:30000"`

3. Follow the standard MinerU setup steps as described above.

With this configuration, RAGFlow will connect to your vLLM server to
perform document parsing, which can significantly improve parsing
performance for complex documents while reducing the resource
requirements on your RAGFlow server.



![1](https://github.com/user-attachments/assets/46624a0c-0f3b-423e-ace8-81801e97a27d)

![2](https://github.com/user-attachments/assets/66ccc004-a598-47d4-93cb-fe176834f83b)


### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update

---------

Co-authored-by: writinwaters <cai.keith@gmail.com>

rag/flow/parser/parser.py

@@ -224,8 +224,9 @@ class Parser(ProcessBase):
             mineru_executable = os.environ.get("MINERU_EXECUTABLE", "mineru")
             mineru_api = os.environ.get("MINERU_APISERVER", "http://host.docker.internal:9987")
             pdf_parser = MinerUParser(mineru_path=mineru_executable, mineru_api=mineru_api)
-            if not pdf_parser.check_installation():
-                raise RuntimeError("MinerU not found. Please install it via: pip install -U 'mineru[core]'.")
+            ok, reason = pdf_parser.check_installation()
+            if not ok:
+                raise RuntimeError(f"MinerU not found or server not accessible: {reason}. Please install it via: pip install -U 'mineru[core]'.")
 
             lines, _ = pdf_parser.parse_pdf(
                 filepath=name,