upgrade kubernetev1.20.15 to v1.21.12 faild

[clcc2019]

What happened:

upgrade kubernetev1.20 to v1.21.12

v1.20.15 sea.hub no coredns:v1.8.0 image，v1.21.12 have

[clcc2019]

coredns imageRepository:

[bxy4543]

The coredns image path is changed to 'core' to 'coredns/coredns' in the v1.21 version, and the same is true in our ${rootfs}/etc/kubeadm.yml file for versions above v1.21, but the image path obtained by upgrade defaults to core, so I think the upgrade needs to specify the config file: kubeadm upgrade ${version} --config ${rootfs}/etc/kubeadm.yml. https://github.com/sealerio/sealer/blob/40103504d817a5e698220dea028fd50d177acc67/pkg/runtime/upgrade.go#L65

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contributing guide

[shy-Xu]

I will try to fix it this weekend.

[shy-Xu]

Would you please tell us the CloudImage you use? both v1.20.15 and v1.21.12 I want to test whether this problems is fixed @clcc2019