BTE occasionally fails to set TTL for cached qEdges

[tokebe]

It's been demonstrated that BTE will occasionally "hold onto" some cached qEdges beyond their expected expire time. The most likely explanation for this is that BTE is failing to set an expire time, likely by way of being restarted prior to the expire time being set.

There is a likely better way to handle this, but as redis does not store key age, the simplest naive approach is to just add a cron job that eliminates all cached qEdges after some interval (once a day at midnight?).

[colleenXu]

I wonder if this is related to #761

EDIT: also linking to our old Slack discussion on this topic and the slack post where @tokebe tried to fix this

[tokebe]

Relevant changes deployed to Prod.