[web] Show VersionUnsupportedModal if QR code auth fails due to unsupported client version

Summary:
I originally noticed that the QR code flow didn't handle this error when investigating ENG-8113. That led to the further realization that the QR code flow hasn't been kept up-to-date, which was addressed in ENG-8123. This diff completes the circle and finally adds code to handle the outdated client error specifically.

Depends on D12124

Test Plan: I hardcoded a failure in keyserver/src/session/version.js for all web clients and saw this error:

Reviewers: bartek

Reviewed By: bartek

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D12125