add China domain region suffix support

[enefry]

Breaking change

support icloud region suffix load from environment variable: icloud_region_suffix

such as :

icloud_region_suffix=.cn
 www.icloud.com.cn

Proposed change

support china icloud support

Type of change

• [x] New feature (which adds functionality to an existing service)

Example of code:

icloud_region_suffix=.cn
 www.icloud.com.cn

Additional information

Checklist

• [x] The code change is tested and works locally.
• [x] Local tests pass. Your PR cannot be merged unless tests pass
• [ ] There is no commented out code in this PR.
• [ ] Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• [x] Documentation added/updated to README