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>

README.md

@@ -37,7 +37,7 @@ By using vLLM Ascend plugin, popular open-source models, including Transformer-l
 - OS: Linux
 - Software:
   * Python >= 3.9, < 3.12
-  * CANN >= 8.0.0
+  * CANN >= 8.1.rc1
   * PyTorch >= 2.5.1, torch-npu >= 2.5.1
   * vLLM (the same version as vllm-ascend)