Complete `merge_queue_entry` and `repository_ruleset` events

The initial scaffolding for [`merge_queue_entry`][1] and [`repository_ruleset`][2] was completed in #329. However, the complete definitions still need to be completed.

[1]: https://docs.github.com/en/webhooks-and-events/webhooks/webhook-events-and-payloads#merge_queue_entry 
[2]: https://docs.github.com/en/webhooks-and-events/webhooks/webhook-events-and-payloads#repository_ruleset 