Support the use of kubeadm to manage etcd and use of existing etcd

[pixiake]

Signed-off-by: pixiake guofeng@yunify.com

What type of PR is this?

/kind feature

What this PR does / why we need it:

At present, kubekey only supports the separate installation of etcd cluster for k8s.
It should also support the use of existing etcd and etcd managed by kubeadm.

Does this PR introduced a user-facing change?

Add some parameters to the configuration file to select etcd cluster installation mode.
Support the choice of three etcd cluster types: kubekey, kubeadm and external.
When the type is set to external, endpoints、caFile、certFile and keyFile should be set..
If TLS authentication is not enabled for the existing etcd, caFile、certFile and keyFile need not be set.

apiVersion: kubekey.kubesphere.io/v1alpha2
kind: Cluster
metadata:
  name: sample
spec:
  ...
  etcd:
    type: external   (kubekey / kubeadm / external)   # default: kubekey
    external:
      endpoints:
      - https://192.168.6.6:2379
      caFile: /pki/etcd/ca.crt
      certFile: /pki/etcd/etcd.crt
      keyFile: /pki/etcd/etcd.key
  ...     

[ks-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pixiake

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[24sama]

/lgtm

[ks-ci-bot]

LGTM label has been added.

Git tree hash: bdf547610b85a2e6ce682c3ab87f36eda8c24b24