Refactor kubeconfig persist logic

[metrue]

Issue:
Summary:

The checklist before PR is ready for review:

• has unit testing for new added codes
• has functional testing for new added features
• has checked the lint or style issues
• README updated if need

[codecov]

Codecov Report

Merging #412 into master will increase coverage by 0.04%.
The diff coverage is 40.81%.

@@            Coverage Diff             @@
##           master     #412      +/-   ##
==========================================
+ Coverage   33.98%   34.03%   +0.04%     
==========================================
  Files          48       48              
  Lines        2189     2192       +3     
==========================================
+ Hits          744      746       +2     
+ Misses       1327     1326       -1     
- Partials      118      120       +2

Impacted Files	Coverage Δ
handlers/infra.go	0% <0%> (ø)	⬆️
middlewares/provision.go	0% <0%> (ø)	⬆️
infra/k8s/cloud.go	54.9% <53.12%> (-0.3%)	⬇️
config/config.go	40.81% <60%> (+1.03%)	⬆️

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