[Doc] Add qwen3 embedding 8b guide (#1734)

1. Add the tutorials for qwen3-embedding-8b
2. Remove VLLM_USE_V1=1  in docs, it's useless any more from 0.9.2


- vLLM version: v0.9.2
- vLLM main:
5923ab9524

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

docs/source/user_guide/feature_guide/sleep_mode.md

@@ -40,7 +40,6 @@ The following is a simple example of how to use sleep mode.
     from vllm.utils import GiB_bytes
 
 
-    os.environ["VLLM_USE_V1"] = "1"
     os.environ["VLLM_USE_MODELSCOPE"] = "True"
     os.environ["VLLM_WORKER_MULTIPROC_METHOD"] = "spawn"
 
@@ -77,7 +76,6 @@ The following is a simple example of how to use sleep mode.
 
     ```bash
     export VLLM_SERVER_DEV_MODE="1"
-    export VLLM_USE_V1="1"
     export VLLM_WORKER_MULTIPROC_METHOD="spawn"
     export VLLM_USE_MODELSCOPE="True"