Copy platform provider kubernetes under the plugin directory

[Warashi]

What this PR does / why we need it:

This PR copies k8s' platform provider implementations under its plugin.
I want to start implementing the Kubernetes plugin by copying the existing platform provider implementations.

Which issue(s) this PR fixes:

Part of #4980

Does this PR introduce a user-facing change?: No

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

Attention: Patch coverage is 21.13668% with 1679 lines in your changes missing coverage. Please review.

Project coverage is 23.93%. Comparing base (38d647a) to head (1555490).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...kg/app/pipedv1/plugin/kubernetes/provider/state.go	0.00%	433 Missing ⚠️
pkg/app/pipedv1/plugin/kubernetes/provider/helm.go	19.93%	232 Missing and 5 partials ⚠️
.../app/pipedv1/plugin/kubernetes/provider/kubectl.go	0.00%	213 Missing ⚠️
.../app/pipedv1/plugin/kubernetes/provider/applier.go	0.00%	167 Missing ⚠️
...app/pipedv1/plugin/kubernetes/provider/manifest.go	27.87%	115 Missing and 4 partials ⚠️
...g/app/pipedv1/plugin/kubernetes/provider/loader.go	11.81%	112 Missing ⚠️
.../pipedv1/plugin/kubernetes/provider/resourcekey.go	27.85%	93 Missing and 8 partials ⚠️
pkg/app/pipedv1/plugin/kubernetes/provider/diff.go	49.74%	87 Missing and 12 partials ⚠️
...ernetes/provider/kubernetestest/kubernetes.mock.go	0.00%	61 Missing ⚠️
.../plugin/kubernetes/provider/chartrepo/chartrepo.go	0.00%	40 Missing ⚠️
... and 6 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5250      +/-   ##
==========================================
- Coverage   24.06%   23.93%   -0.13%     
==========================================
  Files         439      455      +16     
  Lines       46957    49086    +2129     
==========================================
+ Hits        11301    11751     +450     
- Misses      34753    36387    +1634     
- Partials      903      948      +45     

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