Geo: Move file transfer error logs into geo.log

Right now Gitlab::Geo::Transfer#log_transfer_error on the secondary logs a spew of messages in the Rails production.log:

Gitlab::Geo::FileTransfer: Unsuccessful download: 404 Not Found
Gitlab::Geo::LfsTransfer: Unsuccessful download: 404 Not Found
Gitlab::Geo::FileTransfer: Unsuccessful download: 404 Not Found
Gitlab::Geo::FileTransfer: Unsuccessful download: 404 Not Found
Gitlab::Geo::LfsTransfer: Unsuccessful download: 404 Not Found