Necessary for the frontend to be able to paginate easily. Cursor pagination is good for fetching all events, but doesn't play very well when a pagination component gets involved.

Adds support for?offset=x to the existing endpoint. The cursor-based pagination (?after_id=x) is still supported. The two pagination modes are mutually exclusive, and are documented as such. If both are supplied, the request will be rejected.

Also adds atotal property to the response that contains the full count of items matching the filter. We already have indices in place so I don't think this will impact performance (or we can revisit it before GA).