Fix ETCD PKI Provisioning Issue in Karmada Operator

[jabellard]

What type of PR is this?

/kind bug

What this PR does / why we need it:
When provisioning a Karmada instance to be managed by the Karmada operator, there's support for both in-cluster and external ETCD modes. When external ETCD mode is used, the operator should skip setting up an in-cluster ETCD instance, which entails setting up PKI for the instance and deploying it as a stateful set. However, currently, in external ETCD mode, the operator will skip deploying the stateful set, but will still generate PKI, which is an issue. In external ETCD mode, all tasks relevant to setting up an in-cluster instance should be skipped.

Which issue(s) this PR fixes:
Fixes #5975

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

`karmada-operator`: Fixed the issue that external ETCD certificate be overwritten by generated in-cluster ETCD certificate.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 19.35484% with 25 lines in your changes missing coverage. Please review.

Project coverage is 48.25%. Comparing base (c9ca6ac) to head (5a7f917).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
operator/pkg/tasks/init/upload.go	0.00%	19 Missing ⚠️
operator/pkg/certs/certs.go	0.00%	6 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5976      +/-   ##
==========================================
+ Coverage   48.23%   48.25%   +0.01%     
==========================================
  Files         664      664              
  Lines       54749    54753       +4     
==========================================
+ Hits        26410    26419       +9     
+ Misses      26624    26621       -3     
+ Partials     1715     1713       -2     

Flag	Coverage Δ
unittests	48.25% <19.35%> (+0.01%)	⬆️

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[zhzhuang-zju]

Thanks, overall LGTM.

[RainbowMango]

/lgtm
/approve

@jabellard
I assume this has been tested on your side.

In addition, this should be backported to release-1.12 as well, please let me know if you'd like to do it.

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This pull-request has been approved by: RainbowMango

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[jabellard]

/lgtm /approve

@jabellard I assume this has been tested on your side.

In addition, this should be backported to release-1.12 as well, please let me know if you'd like to do it.

Hey @RainbowMango . I just submitted this PR for that.

[RainbowMango]

I see. Thank you.

By the way, we will cut a new alpha release from the master and some patch releases from release branches this week as per the release cycle.