Jira connect /api/:version/repos/:namespace/:project/events API route has SQL n + 1 issues

Discovered as part of gitlab-com/gl-infra/scalability#865 (closed)

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The /api/:version/repos/:namespace/:project/events endpoint, used for JIRA connect, has SQL n+1 problems, resulting sometimes in more than 1000 SQL queries per request.

https://log.gprd.gitlab.net/goto/7900e06c7d8ed9429975b8d8ea230ed2