[keyserver] Print out a QR code to the terminal

Summary:
This diff handles printing out a QR code to the terminal - the idea is that this will ultimately be displayed on the keyserver. For now I've used temporary keys, the next two diffs will encode an ephemeral AES-256 key and the ed25519 key.

Addresses ENG-4776 and ENG-4773.

Depends on D9089

Test Plan:
Confirmed that toggling the flag ensures that the QR code prints out to the terminal

Reviewers: atul, ginsu, varun, patryk

Reviewed By: ginsu

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9180