chore: Optimize access_key description (#71)

Fixes #67 

```release-note
优化`Access Key`相关的描述，减少误解
```

src/main/resources/extensions/policy-template-s3os.yaml

@@ -45,11 +45,13 @@ spec:
  help: 协议头请在上方设置，此处无需以"http://"或"https://"开头，系统会自动拼接
  - $formkit: password
  name: accessKey
- label: Access Key
+ label: Access Key ID
+ placeholder: 存储桶用户标识(用户名)
  validation: required
  - $formkit: password
  name: accessSecret
- label: Access Secret
+ label: Access Key Secret
+ placeholder: 存储桶秘钥(密码)
  validation: required
  - $formkit: text
  name: region