[Stage Plugins] Use METADATA_STAGE_DISPLAY_KEY instead of SkippedBy/ApprovedBy

[t-kikuc]

What this PR does:

• Show the stage metadata by the common key MetadataKey_StageDisplay instead of SkippedBy and ApprovedBy
  • This will be used in k8s plugin too for the trafficPercentage.

Why we need it:

• To suppress hard coding of SkippedBy and ApprovedBy.
  • It reduces tightly-coupled code of web/server/piped/plugin

TODO:

• In the SDK, add pkg/plugin/sdk/constants/constants.go with MetadataKey_StageDisplay
  usage:

import (
   constants "github.com/pipe-cd/piped-plugin-sdk-go/constants"
)

func executeStage(...){
 ...
 client.PutStageMetadata(ctx, constants.MetadataKey_StageDisplay, "Skipped by: user-A")
 ...
}

Which issue(s) this PR fixes:

Fixes Part of #5367

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 (b7555ad) to head (831dee3).
Report is 16 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5980      +/-   ##
==========================================
- Coverage   28.23%   28.16%   -0.07%     
==========================================
  Files         512      516       +4     
  Lines       55326    55895     +569     
==========================================
+ Hits        15620    15745     +125     
- Misses      38461    38898     +437     
- Partials     1245     1252       +7     

Flag	Coverage Δ
.	23.22% <ø> (+<0.01%)	⬆️
.-pkg-app-pipedv1-plugin-kubernetes	66.42% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.51% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-plugin-sdk	50.89% <ø> (ø)
.-tool-actions-gh-release	19.23% <ø> (ø)
.-tool-actions-plan-preview	25.30% <ø> (?)
.-tool-codegen-protoc-gen-auth	0.00% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[ffjlabo]

[IMO] How about defining the const value in the model package to clarify when to use it by grouping related things.
For example, Maybe in pkg/model/stage.go?

BTW, I referred the current implementation.
e.g.
https://github.com/pipe-cd/pipecd/blob/master/pkg/model/deployment.go#L23-L25

[t-kikuc]

it seems good.

Now we don't need to create constants.go.
(I guess MetadataKeyDeploymentNotification will not be used in pipedv1)

tbh, previously the file contained a const for Approvers, which will be used in server too.

[t-kikuc]

@ffjlabo
I moved: 831dee3

[ffjlabo]

@t-kikuc
I got it, thanks!

If this is the stage-specific knowledge, then we might put it in pkg/model/stage.go.
WDYT?

[t-kikuc]

@ffjlabo Oh, I missed stage.go.

But I noticed that stage.go does not seem to be used in pipedv1.
WDYT?

[ffjlabo]

OK, so let's keep it as is.

[ffjlabo]

LGTM

[Warashi]

LGTM