[Analysis Plugin] Add StageStatusSkipped to the SDK

[t-kikuc]

What this PR does:

as title

Why we need it:

to handle manual skipping in the Analysis Plugin

cf. pipedv0:

pipecd/pkg/app/piped/executor/analysis/analysis.go

Lines 114 to 122 in a420da0

	case <-ticker.C:
	if !e.checkSkippedByCmd(ctx) {
	continue
	}
	status = model.StageStatus_STAGE_SKIPPED
	// Stop the context to cancel all running analyses.
	cancel()
	return
	case <-doneCh:

Which issue(s) this PR fixes:

Part of #6068

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):

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 28.68%. Comparing base (45a82f7) to head (934cab5).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6156   +/-   ##
=======================================
  Coverage   28.68%   28.68%           
=======================================
  Files         534      534           
  Lines       57328    57330    +2     
=======================================
+ Hits        16442    16444    +2     
  Misses      39608    39608           
  Partials     1278     1278           

Flag	Coverage Δ
.	23.28% <ø> (ø)
.-pkg-app-pipedv1-plugin-analysis	62.85% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes	62.30% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.48% <ø> (ø)
.-pkg-app-pipedv1-plugin-scriptrun	54.83% <ø> (ø)
.-pkg-app-pipedv1-plugin-terraform	38.31% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-app-pipedv1-plugin-waitapproval	68.62% <ø> (ø)
.-pkg-plugin-sdk	51.03% <100.00%> (+0.04%)	⬆️
.-tool-actions-gh-release	19.23% <ø> (ø)
.-tool-actions-plan-preview	25.30% <ø> (ø)
.-tool-codegen-protoc-gen-auth	0.00% <ø> (ø)

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[Warashi]

🆗

[khanhtc1202]

LGTM 👌