Redact sensitive information from the karmadactl init command output

[zhzhuang-zju]

What type of PR is this?
/kind feature

What this PR does / why we need it:
The karmadactl init command, at the end of the initializtaion, writes some sensitive information in the stdout, like token, in its karmadactl register example. This will bring up two issues：

• data leak, for instance in CI/CD logs
  

• The token's validity period is one day. Users may not join the pull mode member clusters immediately after installing Karmada, causing the secret to expire.

I hope the command output to be how to do rather than what to do. Users can follow the steps in the command output as needed.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
Modified command output:

Register cluster with 'Pull' mode

Step 1: Create bootstrap tokens and get the full 'karmadactl register' flag needed to register the member cluster using the token.
(In karmada)~# karmadactl token create --print-register-command --kubeconfig /etc/init/members/karmada-apiserver.config
karmadactl register [karmada-apiserver-endpoint] --token [token] --discovery-token-ca-cert-hash [ca-cert-hash]

Step 2: Use the output result from step 1 to register the cluster to Karmada control plane. "--cluster-name" is set to cluster of current-context by default.
(In member cluster)~# karmadactl register [karmada-apiserver-endpoint] --token [token] --discovery-token-ca-cert-hash [ca-cert-hash]

Step 3: Show members of karmada
(In karmada)~# karmadactl --kubeconfig /etc/init/members/karmada-apiserver.config get clusters

Does this PR introduce a user-facing change?:

[karmada-bot]

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Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 39.76%. Comparing base (517cb0d) to head (79840e8).

Files with missing lines	Patch %	Lines
pkg/karmadactl/cmdinit/kubernetes/deploy.go	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5714      +/-   ##
==========================================
+ Coverage   39.75%   39.76%   +0.01%     
==========================================
  Files         650      650              
  Lines       55147    55123      -24     
==========================================
- Hits        21924    21922       -2     
+ Misses      31815    31791      -24     
- Partials     1408     1410       +2     

Flag	Coverage Δ
unittests	39.76% <90.90%> (+0.01%)	⬆️

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