Add pipeline IID to pipeline events webhook

Release notes

Problem to solve

As a DevOps engineer creating automation of GitLabCI, I want to be able to use the same pipeline ID from webhook payloads in GraphQL requests so I can simplify my automation code.

Proposal

• Add pipeline_iid to the pipeline events webhook payload.
• Once this is done the project pipeline GraphQL can be use easier.

Intended users

• Sasha (Software Developer)
• Priyanka (Platform Engineer)

Feature Usage Metrics

We'd expect to see an increase in requests to the GraphQL endpoint for pipelineproject with the ID being easier to retrieve.