[feature request] enable yurtctl convert to support k8s v1.19 and 1.21

[Congrool]

What would you like to be added:
Currently, yurtctl convert and revert command cannot support kubernetes v1.19 and v1.21. We should support them. I've run the kubernetes conformance tests based on both two k8s versions, and all cases passed. It's time to enable yurtctl to support v1.19 and v1.21.

Here are the test results.
v1.19

v1.21

others
/kind feature

[Congrool]

Some test details
HostOS: CentOS Linux 7
Kernel Version: 3.10.0-957.el7.x86_64

Openyurt components included:

1. yurthub
2. yurt-tunnel
3. yurt-controller-manager

OpenYurt commit: 61f8a76
OpenYurt deployed with command:

yurtctl convert -c master -t --provider kubeadm \
  --kubeadm-conf-path /usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf \
  --node-servant-image openyurt/node-servant:v0.5.0-amd64-61f8a76  \
  --yurt-controller-manager-image openyurt/yurt-controller-manager:v0.5.0-amd64-61f8a76 \
  --yurt-tunnel-agent-image openyurt/yurt-tunnel-agent:v0.5.0-amd64-61f8a76 \
  --yurt-tunnel-server-image openyurt/yurt-tunnel-server:v0.5.0-amd64-61f8a76 \
  --yurthub-image openyurt/yurthub:v0.5.0-amd64-61f8a76

k8s version: v1.19.13, v1.21.7
Conformance test tool: sonobuoy v0.52.0
Run tests with command:

sonobuoy run --mode=certified-conformance

[rambohe-ch]

@Congrool It's a good job that add conformance test for OpenYurt. and i agree with you that add v1.19 and v1.21 version support.