Feat: vela cluster join support overwrite

[Somefive]

Description of your changes

Previous vela cluster join --name <cluster-name> will report cluster already exist error when the target cluster already exists.

Now it will ask you if you would like to overwrite the old one or pass -y/--yes to overwrite it by default.

$ vela cluster join --name cluster-worker my.kubeconfig                                                                                                                                                            
Cluster already exists, do you want to overwrite it? (y/n)y
Successfully add cluster cluster-worker, endpoint: <endpoint>

I have:

• Read and followed KubeVela's contribution process.
• Related Docs updated properly. In a new feature or configuration option, an update to the documentation is necessary.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Special notes for your reviewer

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[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.03 ⚠️

Comparison is base (784106c) 61.58% compared to head (401da87) 61.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5784      +/-   ##
==========================================
- Coverage   61.58%   61.56%   -0.03%     
==========================================
  Files         217      217              
  Lines       30694    30709      +15     
==========================================
+ Hits        18903    18906       +3     
- Misses      10051    10058       +7     
- Partials     1740     1745       +5     

Flag	Coverage Δ
core-unittests	55.88% <0.00%> (+0.09%)	⬆️
e2e-multicluster-test	25.56% <50.00%> (-0.14%)	⬇️
e2e-rollout-tests	22.27% <0.00%> (-0.02%)	⬇️
e2etests	27.95% <0.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/multicluster/cluster_management.go	38.36% <50.00%> (-0.74%)	⬇️

... and 14 files with indirect coverage changes

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[chivalryq]

LGTM