Refactor kubernetes executors

[nghialv]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[nghialv]

/approve

[pipecd-bot]

This pull request is APPROVED by nghialv.

Approvers can cancel the approval by writing /approve cancel in a comment. Any additional commits also will change this pull request to be not-approved.

[pipecd-bot]

Code coverage for golang is 23.09%. This pull request increases coverage by 0.22%.

File	Function	Base	Head	Diff
pkg/app/piped/executor/kubernetes/baseline.go	Executor.removeBaselineResources	0.00%	0.00%	+0.00%
pkg/app/piped/executor/kubernetes/canary.go	Executor.removeCanaryResources	0.00%	0.00%	+0.00%
pkg/app/piped/executor/kubernetes/traffic.go	Executor.generateTrafficRoutingManifest	0.00%	0.00%	+0.00%
pkg/app/piped/executor/kubernetes/kubernetes.go	makeSuffixedName	66.67%	100.00%	+33.33%
pkg/app/piped/executor/kubernetes/traffic.go	Executor.ensureTrafficRouting	0.00%	0.00%	+0.00%
pkg/app/piped/executor/kubernetes/traffic.go	generateVirtualServiceManifest	88.46%	86.21%	-2.25%
pkg/app/piped/executor/kubernetes/traffic.go	generateVirtualServiceManifestV1Alpha3	0.00%	0.00%	+0.00%
pkg/app/piped/cloudprovider/kubernetes/manifest.go	Manifest.Duplicate	0.00%	100.00%	+100.00%
pkg/app/piped/executor/kubernetes/kubernetes.go	Executor.deleteResources	0.00%	0.00%	+0.00%
pkg/app/piped/executor/kubernetes/kubernetes.go	duplicateManifest	0.00%	100.00%	+100.00%