`Authorization` headers not passed properly through Api Gateway v1.

When attempting to pass `Authorization` headers, its accessible via `events.headers` directly, but not through the `event` object via `event.headers`. Seems to be related to #437 #464.

The patch suggested by #437 seems to work as expected, but would like to see this implemented into this library.

Start by tracing the API Gateway v1 request adapter that builds event.headers, then compare it with the events.headers path described in the issue and review related issues #437 and #464. Done means Authorization is available through event.headers as well as events.headers, with the behavior verified by the project's existing tests.

Scritto dal modello di indicizzazione a partire dal testo della issue.