Upgrade CANN version to 8.1.rc1 (#747)

### What this PR does / why we need it?

Make CANN version bump separately from
https://github.com/vllm-project/vllm-ascend/pull/708

- Upgrade CANN version to 8.1.rc1
- Add prefix to speed up download
`m.daocloud.io/quay.io/ascend/cann:8.1.rc1-910b-ubuntu22.04-py3.10`
- Address tail sapce for Dockerfile.openEuler
- Add note for `/workspace` and `/vllm-workspace` as followup of
https://github.com/vllm-project/vllm-ascend/pull/741

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?

CI passed

Co-authored-by: MengqingCao <cmq0113@163.com>

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>
Co-authored-by: MengqingCao <cmq0113@163.com>

Dockerfile.openEuler

@@ -15,7 +15,7 @@
 # This file is a part of the vllm-ascend project.
 #
 
-FROM quay.io/ascend/cann:8.0.0-910b-openeuler22.03-py3.10
+FROM quay.io/ascend/cann:8.1.rc1-910b-openeuler22.03-py3.10
 
 ARG PIP_INDEX_URL="https://mirrors.tuna.tsinghua.edu.cn/pypi/web/simple"
 ARG COMPILE_CUSTOM_KERNELS=1
@@ -30,7 +30,7 @@ RUN pip config set global.index-url ${PIP_INDEX_URL}
 
 WORKDIR /workspace
 
-COPY . /vllm-workspace/vllm-ascend/  
+COPY . /vllm-workspace/vllm-ascend/
 
 # Install vLLM
 ARG VLLM_REPO=https://github.com/vllm-project/vllm.git
@@ -53,4 +53,4 @@ RUN source /usr/local/Ascend/ascend-toolkit/set_env.sh && \
 RUN python3 -m pip install modelscope ray && \
     python3 -m pip cache purge
 
-CMD ["/bin/bash"]
+CMD ["/bin/bash"]