Implement BuildPipelineSyncStages for k8s multi sync

[ffjlabo]

What this PR does:

as title.

I checked the behavior with planning pipeline sync. It is ok to fail the execution because I don't implement its logic.

apiVersion: pipecd.dev/v1beta1
kind: Application
spec:
  name: multicluster-plugin
  labels:
    env: example
    team: product
  planner:
    alwaysUsePipeline: true
  quickSync:
    prune: true
  pipeline:
    stages:
        - name: K8S_SYNC
  input:
    kubectlVersion: 1.31.0
  description: |
    try multi cluster plugin
  plugins:
    - kubernetes_multicluster

Why we need it:

Which issue(s) this PR fixes:

Part of #5006

Does this PR introduce a user-facing change?:

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

[ffjlabo]

borrowed these code from k8s plugin

[codecov]

Codecov Report

Attention: Patch coverage is 81.25000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 26.26%. Comparing base (a20eaef) to head (8c98e8a).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
...p/pipedv1/plugin/kubernetes_multicluster/plugin.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5596      +/-   ##
==========================================
+ Coverage   26.24%   26.26%   +0.02%     
==========================================
  Files         472      474       +2     
  Lines       50428    50475      +47     
==========================================
+ Hits        13234    13259      +25     
- Misses      36134    36153      +19     
- Partials     1060     1063       +3     

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[Warashi]

Almost LGTM. I commented on nits.

[Warashi]

There seems to be no predefined stage and no copy.

Suggested change

// we copy the predefined stage to avoid modifying the original one.

[ffjlabo]

Thanks, fixed on 4a9ce2f

[Warashi]

It might be forgotten to change the comment.

Suggested change

	// StageK8sSync represents the state where
	// all resources should be synced with the Git state.
	StageK8sMultiSync string = "K8S_MULTI_SYNC"
	// StageK8sRollback represents the state where all deployed resources should be rollbacked.
	StageK8sMultiRollback string = "K8S_MULTI_ROLLBACK"
	// StageK8sMultiSync represents the state where
	// all resources should be synced with the Git state.
	StageK8sMultiSync string = "K8S_MULTI_SYNC"
	// StageK8sMultiRollback represents the state where all deployed resources should be rollbacked.
	StageK8sMultiRollback string = "K8S_MULTI_ROLLBACK"

[ffjlabo]

Thanks, fixed on 4a9ce2f

[Warashi]

It's nice to have t.Parallel() here.

Suggested change

	t.Run(tt.name, func(t *testing.T) {
	actual := BuildPipelineStages(tt.input)
	t.Run(tt.name, func(t *testing.T) {
	t.Parallel()
	actual := BuildPipelineStages(tt.input)

[ffjlabo]

Thanks, fixed on
8c98e8a

[Warashi]

👍🏻

[Warashi]

LGTM

[t-kikuc]

LGTM, Go Go!