Parsing events in handler review

We need to review the `parse_event()` function and also the code at the beginning of each handler to make it more robust against missing fields.

The current phrasing of the event strips everything except the body and request context but we are actually using and needs more than that which comes from the http gateway like path information.

This needs to be more robust if we plan on adding in other sources of events such as EventBridge into the same handlers before routing them.