feat(github): support payload field on Deployment notifications

[aydabd]

Summary

Add a templated Payload field on GitHubDeployment so trigger templates can carry deploy-time metadata (image tag, build id, etc.) into the GitHub deployment record. The field maps to GitHub's CreateDeployment API payload parameter — a JSON text the API explicitly exposes for this purpose, today silently dropped by notifications-engine.

Why

Downstream consumers of the deployment_status event (workflows, Slack handlers, audit tooling) often need to know what was deployed (image tag, immutable artifact id). Without a templated payload, the field is always {} and consumers have to fall back to indirect lookups (e.g. git tag --points-at <sha>).

Changes

• Add Payload string to GitHubDeployment.
• Parse and execute the field as a Go template in GetTemplater.
• Pass the rendered string to DeploymentRequest.Payload when present.
• Extend TestGetTemplater_GitHub_Deployment to cover templated payload rendering.
• Document the new field in docs/services/github.md.

Example

template.app-deployed: |
  github:
    repoURLPath: "{{.app.spec.source.repoURL}}"
    revisionPath: "{{.app.status.operationState.syncResult.revision}}"
    deployment:
      state: success
      environment: production
      payload: |
        {"image": "registry/app:{{.app.status.sync.revision}}"}

Closes #443

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds support for providing a templated payload in GitHub deployment notifications and passing it through to GitHub’s Create Deployment API.

Changes:

• Extend GitHubDeployment to include a payload field.
• Template and render the deployment payload alongside existing deployment fields.
• Document the new payload option and add a unit test assertion for payload templating.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
pkg/services/github.go	Adds Payload to deployment model, templates it, and forwards it into github.DeploymentRequest.
pkg/services/github_test.go	Extends templater test to cover payload rendering.
docs/services/github.md	Documents new payload configuration for GitHub deployments.

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[codecov]

Codecov Report

❌ Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.13%. Comparing base (da04400) to head (d83fe76).
⚠️ Report is 37 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/services/github.go	76.47%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #451      +/-   ##
==========================================
+ Coverage   55.41%   58.13%   +2.71%     
==========================================
  Files          46       49       +3     
  Lines        4125     3791     -334     
==========================================
- Hits         2286     2204      -82     
+ Misses       1511     1222     -289     
- Partials      328      365      +37     

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