Cron job to clear search

[the-codetrane]

Problem

We persist search objects and need a manner by which to vacate old search data

Solution

• write a rake task to vacate searches that are a week old
• use whenever to create a scheduled cron job

PR Type

• Feature
• Tests
• Janitorial (refactoring, dependency updates, etc.)

[the-codetrane]

This PR is to create the whenever schedule and rake task. We'll need to find a way to invoke whenever to write to the cron tab on the box on deploy:

[mnyrop]

@the-codetrane Looks good to me! Since this'll interact with the mysql DB on prod (and we don't have testing for it), my inclination would be to ship this in a standalone tag and make sure it works properly isolated from the other changes. With that in mind, is OK if we keep this PR in the hopper for a later deploy? Also open to opinions from @dxu1789