"Update available" flow

[rohitpaulk]

🚧 WIP

Problem

We occasionally need to ship backend changes that are incompatible with new frontend versions.

How we handle this currently

Until now our approach has been to keep changes backward compatible for a week or so, and then remove the backward compatibility code after.

Requirements

We'd like to have a way to notify users that an update is available. We don't want to do this on every update, only on ones that where we manually make a version bump.