Add (work item) type to issue events webhook

Problem

There's currently nothing in the issue payload to help identify an incident issue.

Customer Use Case

Customers with external ITSM providers use the Issue Events webhook to automatically integrate their incident management with GitLab to take full advantage of our DORA metrics. To do this, they need a reliable way to differentiate between different issue types.

Proposal

Add to Gitlab::HookData::IssueBuilder to include something to identify the type of issue, so that an incident can be identified.

Release notes

Issues, tasks, incidents, requirements, objectives, and key results all trigger payloads under the Issues Events webhook category. Until now, there has been no way to quickly determine the type of object that triggered the webhook within the event payload. This release introduces an object_attributes.type attribute available on payloads within the Issues events, Comments, Confidential issues events, and Emoji events triggers.

https://docs.gitlab.com/ee/user/project/integrations/webhook_events.html#issue-events