Improve broadcast message cache management

Ohhh I got it. During failover, the secondary becomes a primary, and the cache key expiration becomes indefinite again.

So this only affects instances that are demoted from primary to secondary. 😢

I'll create an issue for that in EE, which I feel could be done post migration.

On a related note, should we add a migration to clear this key in any case?

That would be fine, although due to the above, I think we may as well resolve it at the same time in the caching logic. I.e. Maybe there is a good spot to delete the cache key that would resolve all of this.