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?:

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Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 46.24%. Comparing base (72cfef5) to head (429f2d3).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
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@@            Coverage Diff             @@
##           master    #5714      +/-   ##
==========================================
+ Coverage   46.18%   46.24%   +0.05%     
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  Lines       54592    54575      -17     
==========================================
+ Hits        25215    25236      +21     
+ Misses      27752    27717      -35     
+ Partials     1625     1622       -3     

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[zhzhuang-zju]

/assign @RainbowMango

[RainbowMango]

OK. Please rebase the code to make the new tests happy.

[RainbowMango]

Something like:

Step 1: Create bootstrap token and generate the '%[2]s register' command which will be used later.
~# %[2]s token create --print-register-command --kubeconfig=<path-to-karmada-config>
This command will generate a registration command similar to:

%[2]s register 172.18.0.5:5443 --token t8xfio.640u9gp9obc72v5d --discovery-token-ca-cert-hash sha256:9cfa542ff48f43793d1816b1dd0a78ad574e349d8f6e005e6e32e8ab528e4244

Step 2: Use the output from Step 1 to register the cluster to the Karmada control plane. 
You need to specify the target member cluster by flag '--kubeconfig'
~# %[2]s register 172.18.0.5:5443 --token t8xfio.640u9gp9obc72v5d --discovery-token-ca-cert-hash sha256:9cfa542ff48f43793d1816b1dd0a78ad574e349d8f6e005e6e32e8ab528e4244 --kubeconfig=<path-to-member-cluster-kubeconfig>

Step 3: Show members of Karmada
~# %[2]s --kubeconfig=<path-to-karmada-config> get clusters

The %[2]s register command has several optional parameters for setting the properties of the member cluster. For more details, run:

~# %[2]s register --help

[zhzhuang-zju]

Since this is an example of karmadactl init, path-to-karmada-config is deterministic and can be referred to directly by %[1]s/karmada-apiserver.config

[RainbowMango]

/lgtm
/approve

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