Feature request: Allow passing the API key via a different header

[veimox]

The current setup requires the user to pass the Authorization header which limits the flexibility on the deployment patterns, as we might deploy the container behind fx an API gateway that requires or uses that header. It would be ideal to remove this limitation by either

1. Option A: Allow to override the lookup header with a new environment variable such as PDP_AUTH_HEADER that defaults to Authorization.
2. Option B: Allow to read the API Key from a industry standard custom X-Header such as X-PDP-API-KEY that won't collide with the standard header and it will always take preference if defined.