Download a specific multimedia file for a given application.

Authentication: Supports two methods:

1. Traditional: Authorization header (ServerKey/Bearer tokens)
2. JWT query parameter (for external integrations like iagen/pathbot)

When JWT is provided, it is validated against the multimedia resource.

Byte-range requests: Supports partial content downloads via the Range header.
When a valid Range header is provided, the server responds with 206 Partial Content
and streams only the requested byte range from Google Cloud Storage.

The partial content response includes the Content-Range header, which indicates
the returned byte range and the total file size, as well as Accept-Ranges: bytes.

Ex:
Range: bytes=0-1048575 to download the first 1MB of the multimedia file.
Content-Range: bytes 0-1048575/5242880 indicates that the response contains bytes 0-1048575 of a total 5242880 bytes file.