introduce kubectl plugin

[XiShanYongYe-Chang]

Signed-off-by: changzhen changzhen5@huawei.com

What type of PR is this?

/kind feature

What this PR does / why we need it:

Support kubectl karmada plugin.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

# kubectl karmada -h
kubectl karmada controls a Kubernetes Cluster Federation.

Usage:
  karmada [flags]
  karmada [command]

Available Commands:
  cordon      Mark cluster as unschedulable
  help        Help about any command
  join        Register a cluster to control plane
  uncordon    Mark cluster as schedulable
  unjoin      Remove the registration of a cluster from control plane
  version     Print the version info

Flags:
      --add-dir-header                   If true, adds the file directory to the header of the log messages
      --alsologtostderr                  log to standard error as well as files
  -h, --help                             help for karmada
      --kubeconfig string                Paths to a kubeconfig. Only required if out-of-cluster.
      --log-backtrace-at traceLocation   when logging hits line file:N, emit a stack trace (default :0)
      --log-dir string                   If non-empty, write log files in this directory
      --log-file string                  If non-empty, use this log file
      --log-file-max-size uint           Defines the maximum size a log file can grow to. Unit is megabytes. If the value is 0, the maximum file size is unlimited. (default 1800)
      --log-flush-frequency duration     Maximum number of seconds between log flushes (default 5s)
      --logtostderr                      log to standard error instead of files (default true)
      --one-output                       If true, only write logs to their native severity level (vs also writing to each lower severity level)
      --skip-headers                     If true, avoid header prefixes in the log messages
      --skip-log-headers                 If true, avoid headers when opening log files
      --stderrthreshold severity         logs at or above this threshold go to stderr (default 2)
  -v, --v Level                          number for the log level verbosity
      --vmodule moduleSpec               comma-separated list of pattern=N settings for file-filtered logging

Use "karmada [command] --help" for more information about a command.

# kubectl karmada version
kubectl karmada version: version.Info{GitVersion:"v0.8.0-60-g5250689", GitCommit:"5250689ebc9e8e7b67e5055f6f38c28a3c6d8a45", GitTreeState:"clean", BuildDate:"2021-09-01T10:02:37Z", GoVersion:"go1.16", Compiler:"gc", Platform:"linux/amd64"}

Does this PR introduce a user-facing change?:

User can use `kubectl karmada` command, this command is the same as that of karmadactl.

[RainbowMango]

Is there a smart way to share code between karmadactl and kubectl-karmada?

[RainbowMango]

/lgtm
/approve

[RainbowMango]

Hi @XiShanYongYe-Chang Please resolve the conflicts...

/hold
/retitle introduce kubectl plugin

[XiShanYongYe-Chang]

Hi @XiShanYongYe-Chang Please resolve the conflicts...

Resolved. Please have a look again.

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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This pull-request has been approved by: RainbowMango

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[RainbowMango]

/lgtm
/hold cancel