Can you support `merge_group` event in plan-preview-action ?

What would you like to be added:

I would like you to support the merge_group event in plan-preview-action.

Why is this needed:

My project is using merge queue.

Merge queue is failed with this error:

unexpected event merge_group, only "pull_request", "issue_comment" and "push" event are supported

Reference:

https://github.com/pipe-cd/pipecd/blob/7b471d7a9f2eb09ccbc0a9222b6e7adb08ea2edf/tool/actions-plan-preview/main.go#L231-L233