template: export GroupKey on template.Data

[locker95]

Pull Request Checklist

• Please list all open issue(s) discussed with maintainers related to this change
  • Fixes template.Data does not export GroupKey #2526
• Is this a new Receiver integration?
  • N/A
• Is this a bug fix?
  • I have added tests that can reproduce the bug which pass with this bug fix applied
• Is this a new feature?
  • N/A (small API completeness fix)
• Does this change affect performance?
  • N/A
• Is this a breaking change?
  • My changes do not break the existing cluster messages
  • My changes do not break the existing api
• I have added/updated the required documentation
• I have signed-off my commits
• I will follow best practices for contributing to this project

Summary

template.Data did not export GroupKey, even though the webhook JSON payload has always included groupKey. Webhook receivers that reuse template.Data (or custom templates that need the grouping key) had no way to access it without defining their own struct.

This change:

1. Adds GroupKey to template.Data with JSON tag groupKey (matching the documented webhook field).
2. Populates it from the notify context in GetTemplateData when a group key is present.
3. Adds unit tests for population and template access via {{ .GroupKey }}.

The webhook Message type still sets its own GroupKey field for the wire format; Go's encoding/json prefers the outer field, so the payload is unchanged.

Which user-facing changes does this PR introduce?

[ENHANCEMENT] template: Export GroupKey on template.Data for templates and webhook-style consumers. #2526

[coderabbitai]

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ℹ️ Recent review info

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Plan: Enterprise

Run ID: 29dc9ed3-d31b-4a5a-beaf-79b75e3a23e6

📥 Commits

Reviewing files that changed from the base of the PR and between 949777a and 4979805.

📒 Files selected for processing (3)

• notify/util.go
• notify/util_test.go
• template/template.go

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📝 Walkthrough

Walkthrough

Adds GroupKey to template data, populates it from notification context, and tests propagation, template access, JSON naming, and empty behavior when absent.

Changes

GroupKey propagation

Layer / File(s)	Summary
Template data contract template/template.go	Adds the exported Data.GroupKey field with json:"groupKey" serialization.
Context propagation and validation notify/util.go, notify/util_test.go	Copies an available context group key into template data and tests propagation, template access, and missing-key behavior.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately describes exporting GroupKey on template.Data.
Description check	✅ Passed	The PR description includes the checklist, summary, issue reference, and release notes, and is mostly complete.
Linked Issues check	✅ Passed	The change exports GroupKey and populates it in template.Data, matching issue #2526's request.
Out of Scope Changes check	✅ Passed	The diff stays focused on template.Data, notify propagation, and tests, with no unrelated changes evident.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[TheMeier]

Just for the record:
one will not be able to use it in custom webhook payload templates see #5012. This could be mitigated by custom handling in renderPayload

Also the groupKey is not unique #3817.