Define PlanPreviewService proto

[t-kikuc]

What this PR does:

as title

Note

• The API is based on here:

  pipecd/pkg/app/piped/planpreview/builder.go

  Lines 245 to 260 in b7555ad

  	switch app.Kind {
  	case model.ApplicationKind_KUBERNETES:
  	dr, err = b.kubernetesDiff(ctx, app, targetDSP, preCommit, &buf)
  	case model.ApplicationKind_TERRAFORM:
  	dr, err = b.terraformDiff(ctx, app, targetDSP, &buf)
  	case model.ApplicationKind_CLOUDRUN:
  	dr, err = b.cloudrundiff(ctx, app, targetDSP, preCommit, &buf)
  	case model.ApplicationKind_ECS:
  	dr, err = b.ecsdiff(ctx, app, targetDSP, preCommit, &buf)
  	case model.ApplicationKind_LAMBDA:
  	dr, err = b.lambdadiff(ctx, app, targetDSP, preCommit, &buf)
  	default:
  	dr = &diffResult{
  	summary: fmt.Sprintf("%s application is not implemented yet (coming soon)", app.Kind.String()),
  	}
  	}

• GetPlanPreviewResponse.details is bytes for faster communication. SDK will serve a buffered writer to plugin developers.
• Please add new fields of application to GetPlanPreviewRequest while implementing the k8s plugin. Others will only use application_id.
• At first, we won't pass RunningDeploySource because it's better to compare TargetDeploySource and LiveState.
  • In the future, we might add RunningDeploySource to GetPlanPreviewRequest or add a new rpc.

Why we need it:

To start developing Piped-side and the SDK of PlanPreview

Which issue(s) this PR fixes:

Part of #5985

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 28.16%. Comparing base (19aed96) to head (bfb485d).
Report is 35 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5986      +/-   ##
==========================================
- Coverage   28.49%   28.16%   -0.34%     
==========================================
  Files         520      516       -4     
  Lines       56436    55933     -503     
==========================================
- Hits        16082    15754     -328     
+ Misses      39087    38925     -162     
+ Partials     1267     1254      -13     

Flag	Coverage Δ
.	23.22% <ø> (-0.58%)	⬇️
.-pkg-app-pipedv1-plugin-example	?
.-pkg-app-pipedv1-plugin-kubernetes	66.42% <ø> (+0.01%)	⬆️
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.51% <ø> (+0.01%)	⬆️
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-plugin-sdk	50.89% <ø> (+2.03%)	⬆️
.-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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[t-kikuc]

For now, we'll focus on comparing with LiveState, not with RunningDeploymentSource.
If they're needed in the future, let's define a new v2 interface of the PlanPreviewService.

[ffjlabo]

LGTM

[Warashi]

LGTM