br: modify to use one kubeconfig for multiple data planes (#5186)

[ti-chi-bot]

This is an automated cherry-pick of #5186

What problem does this PR solve?

Modify to use one kubeconfig for multiple data planes

Closes #5183

What is changed and how does it work?

Change the flag federation-kubeconfig-path to the kubeconfig file path. Then read the kubeconfig file and use the contexts in kubeconfig file mapping to the data planes

After this change, the secret that stores the kubeconfig file should be configured like this:

apiVersion: v1
kind: Secret
metadata:
  name: br-federation-kubeconfig
type: Opaque
data:
  kubeconfig: {encoded-kubeconfig}

If the user want to use custom secret name or custom data key, he should change the value of chart .brFederationManager.federationKubeconfigSecret or .brFederationManager.federationKubeconfigSecretKey

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[codecov-commenter]

Codecov Report

Merging #5209 (9832290) into release-1.5 (d775285) will increase coverage by 0.00%.
The diff coverage is 0.00%.

Additional details and impacted files

@@             Coverage Diff              @@
##           release-1.5    #5209   +/-   ##
============================================
  Coverage        57.93%   57.94%           
============================================
  Files              248      248           
  Lines            29343    29343           
============================================
+ Hits             17001    17003    +2     
+ Misses           10693    10692    -1     
+ Partials          1649     1648    -1     

Flag	Coverage Δ
unittest	57.94% <0.00%> (+<0.01%)	⬆️

[ti-chi-bot]

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