Use `withdrawal-id` instead of `withdrawal_id` in events

[obycode]

There is an inconsistency in the naming of withdrawal_id. Since other event data is coming from Clarity, the standard is to use kebab-case. The withdrawal event should be updated to follow this standard.

Note that this will require a synchronized change with the API.

[zone117x]

This particular event property isn't being explicitly extracted in the API codebase right now. So feel free to make this change without worrying about breakage on the API-side 👍