Fix #1568 by cleaning job logs older than 7 days

Fixes #1568 

# Test Notes
* Check the current status of the "wad-joblogs" container on the diagnostics storage account (which is the same as the normal storage account for non-Prod environments). We should see logs that are MORE than 7 days old.
* Deploy the worker to QA/Staging/etc. (NOTE: Staging has not really had an active worker so while it should be updated, it'll be difficult to test)
* Within a few minutes, the jobs should clear down to 7 days. If not, let @anurse know. It may take 12 hours to clean down