Add authentication option via `Proxy-Authorization: Bearer xxxx`

[ecerulm]

I have Airbyte deployed behind a Google Cloud Platform IAP proxy (Identity-Aware Proxy).

I need to pass a token (generated with gcloud auth print-identity-token) in the HTTP header Proxy-Authentication: Bearer XXX in order to reach the Airbyte API (I have this setup working with curl / Postman).

Adding support to pass a proxy_bearer_auth in the same way that is possible to pass a bearer_auth it would enable this use case (API behind GCP IAP).