jira: allow disabling label updates via labels.enable_update

[Drenovik]

What changed

• notify/jira/config.go: JiraLabelsConfig gains EnableUpdate *bool and Values []string;
  a custom UnmarshalYAML accepts both the legacy labels: [a, b] list and a new object
  form labels: { enable_update: false, values: [...] }. EnableUpdateValue() defaults
  to true when unset (matches the enable_update pattern already used for
  summary/description in Jira Integration: Allow configuring issue update via parameter #4621).
• notify/jira/jira.go: on issue update (HTTP PUT), if enable_update resolves to false,
  Fields.Labels is set to nil (not an empty slice) so the JSON labels key is omitted
  entirely - manually added / automation-added Jira labels are left untouched. Issue
  creation (POST) is unaffected and always sets labels.
• Docs (docs/configuration.md) and CHANGELOG.md updated.

Why

Every notifier PUT today fully replaces fields.labels, silently wiping labels added by
a human or by Jira automation after issue creation - a known migration issue coming
from jiralert (which never updated labels post-create). This mirrors the existing
enable_update pattern for summary/description (#4621) rather than inventing a new
mechanism.

Backward compatibility

The legacy labels: [a, b] YAML list keeps working unchanged - enable_update defaults
to true, so existing configs see identical behavior (labels are still replaced on
every update, as before). Only configs that opt into the new object form and
explicitly set enable_update: false see a behavior change.

Testing

• Unit tests: go test ./notify/jira/ ./config/ -count=1 - new/updated cases cover:
  legacy list unmarshal, object-form unmarshal (both flag values), create always sets
  labels, update with enable_update true (labels replaced) and false (labels omitted
  from the request body).
• Config loading: amtool check-config against a new fixture using the legacy labels
  list form - confirms no regression in config parsing for existing users.
• Manual end-to-end testing against a private Jira Data Center instance: created an
  issue, manually added a label unrelated to the Alertmanager config, then triggered
  an update. With enable_update unset (legacy default), the manually added label was
  removed (expected baseline, matches current released behavior). With
  enable_update: false, the manually added label survived the update.

Pull Request Checklist

Please check all the applicable boxes.

• Please list all open issue(s) discussed with maintainers related to this change
  • Related to Jira Integration: Allow configuring issue update via parameter #4621, Jira: Add option to disable issue updates #4297
• Is this a new Receiver integration?
  • N/A - existing jira_configs receiver, not a new receiver type
• Is this a bugfix?
  • N/A - this is not a bugfix
• Is this a new feature?
  • I have added tests that test the new feature's functionality
• Does this change affect performance?
  • N/A - no performance-sensitive path touched
• 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

Which user-facing changes does this PR introduce?

[ENHANCEMENT] jira: Allow disabling label updates on existing issues via labels.enable_update (legacy labels list unchanged).

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Review profile: CHILL

Plan: Pro Plus

Run ID: 47facd0f-0328-4bb9-90e8-1f3c897b05f2

📥 Commits

Reviewing files that changed from the base of the PR and between 8d7515a and d4459b0.

📒 Files selected for processing (7)

• CHANGELOG.md
• config/config_test.go
• config/testdata/conf.jira-legacy-labels.yml
• docs/configuration.md
• notify/jira/config.go
• notify/jira/jira.go
• notify/jira/jira_test.go

---

📝 Walkthrough

Walkthrough

Jira label configuration now supports legacy lists and an object form with values and enable_update. Label updates can be disabled for existing issues while labels remain included during issue creation. Tests and documentation cover parsing and request behavior.

Changes

Jira label update control

Layer / File(s)	Summary
Jira label configuration contract notify/jira/config.go, config/testdata/conf.jira-legacy-labels.yml, config/config_test.go	JiraLabelsConfig stores label values and the optional update flag. YAML parsing accepts both list and object forms.
Jira label update behavior notify/jira/jira.go	The notifier uses Labels.Values and omits labels from existing-issue updates when updates are disabled. Creation requests still include labels.
Label behavior validation and documentation notify/jira/jira_test.go, docs/configuration.md, CHANGELOG.md	Tests cover YAML parsing, creation, and existing-issue updates. Documentation and the changelog describe the new configuration forms and behavior.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant JiraNotifier
  participant JiraLabelsConfig
  participant JiraAPI
  JiraNotifier->>JiraLabelsConfig: read Values and EnableUpdateValue()
  alt creating an issue
    JiraNotifier->>JiraAPI: send creation request with labels
  else updating an existing issue
    JiraNotifier->>JiraAPI: send update request without labels when updates are disabled
  end

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the Jira notifier change and the new labels.enable_update option.
Description check	✅ Passed	The description explains the change, rationale, compatibility, testing, documentation, release notes, and checklist status.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests

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[Drenovik]

CodeRabbit’s Docstring Coverage warning is about the new JiraLabelsConfig.EnableUpdateValue method, which has no godoc — matching the existing JiraFieldConfig.EnableUpdateValue in the same file.