make pull cluster to be able to register with proxy-server

[yanfeng1992]

What type of PR is this?
/kind feature

What this PR does / why we need it:

make pull cluster to be able to register with proxy-server

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

`karmadactl`: Introduced `--proxy-server-address` flag to `register` command to declare proxy server during registering a cluster.

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (7c76237) 53.83% compared to head (d8a7d89) 53.84%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4076   +/-   ##
=======================================
  Coverage   53.83%   53.84%           
=======================================
  Files         231      231           
  Lines       23062    23062           
=======================================
+ Hits        12415    12417    +2     
+ Misses       9970     9968    -2     
  Partials      677      677           

Flag	Coverage Δ
unittests	53.84% <ø> (+<0.01%)	⬆️

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see 1 file with indirect coverage changes

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[RainbowMango]

Looks good to me. Have you tested it?

Are you using karmadactl register in your company? Just curious about it. :)

[yanfeng1992]

@RainbowMango

Are you using karmadactl register in your company?

We did not use karmadactl directly. We used the logic of karmadactl register in our multi-cluster-operator to implement the join pull cluster, and used the logic of karmadactl join to implement the join push cluster.

Have you tested it?

Deployed karmada agent and anp agent in the member cluster

Deployed anpserver in the host cluster

member cluster join successful

Member cluster resources can be accessed through the karmada proxy function

[RainbowMango]

/lgtm
/approve

Thanks.

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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