Add Alibaba Cloud Container Registry

[denverdino]

Signed-off-by: Li Yi denverdino@gmail.com

I have tested cosign for Alibaba Cloud Container Registry and work!

My verify result:

$ cosign sign -key cosign.key registry.cn-hangzhou.aliyuncs.com/denverdino/busybox
Enter password for private key:
Pushing signature to: registry.cn-hangzhou.aliyuncs.com/denverdino/busybox:sha256-dca71257cd2e72840a21f0323234bb2e33fea6d949fa0f21c5102146f583486b.sig

$ cosign verify -key cosign.pub registry.cn-hangzhou.aliyuncs.com/denverdino/busybox

Verification for registry.cn-hangzhou.aliyuncs.com/denverdino/busybox --
The following checks were performed on each of these signatures:
  - The cosign claims were validated
  - The signatures were verified against the specified public key
  - Any certificates were verified against the Fulcio roots.
{"critical":{"identity":{"docker-reference":"registry.cn-hangzhou.aliyuncs.com/denverdino/busybox"},"image":{"docker-manifest-digest":"sha256:dca71257cd2e72840a21f0323234bb2e33fea6d949fa0f21c5102146f583486b"},"type":"cosign container image signature"},"optional":null}

Based on: #40