Add Jira integration properties support

Closes #2199 (closed)

I prefer to create each integration as a separate issue for simplicity, to keep the code as small as possible, and to give other contributors a chance to contribute to these issues!

Following the approach discussed here !2670 (merged)

This is what the API returns

curl -s -X PUT "${API_URL}/groups/${GROUP_ID}/integrations/jira" \
  -H "PRIVATE-TOKEN: ${GITLAB_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{
    "url":"https://jira.example.com",
    "username":"testuser",
    "password":"testpass"
  }' | jq .

{
  "id": 48,
  "title": "Jira issues",
  "slug": "jira",
  "created_at": "2026-01-23T08:19:02.417Z",
  "updated_at": "2026-01-23T08:19:02.417Z",
  "active": true,
  "commit_events": true,
  "push_events": true,
  "issues_events": true,
  "incident_events": false,
  "alert_events": true,
  "confidential_issues_events": true,
  "merge_requests_events": true,
  "tag_push_events": true,
  "deployment_events": false,
  "note_events": true,
  "confidential_note_events": true,
  "pipeline_events": true,
  "wiki_page_events": true,
  "job_events": true,
  "comment_on_event_enabled": true,
  "inherited": false,
  "properties": {
    "url": "https://jira.example.com",
    "api_url": null,
    "jira_auth_type": 0,
    "username": "testuser",
    "jira_issue_regex": null,
    "jira_issue_prefix": null,
    "jira_issue_transition_id": null,
    "issues_enabled": false,
    "project_keys": []
  }
}

Part of: Epic #2198 - Refactor Integration Get*Settings Breaking Change: New methods added to IntegrationsServiceInterface