Configure whenever_roles so cron jobs are installed where we expect them

[corylown]

Removing this db role from some of the searchworks webapp VMs had the side effect of revealing that we hadn't configured the whenever_roles. See the whenever docs: https://github.com/javan/whenever?tab=readme-ov-file#capistrano-roles:

However, if you want to restrict certain jobs to only run on subset of servers, you can add a roles: [...] argument to their definitions. Make sure to add that role to the whenever_roles list in your deploy.rb.

Turns out if you don't add the roles you're using the the whenever_roles list the cron jobs are added all of the VMs with the db role by default.

I think there's more cleanup we could do (I'll put up separate PRs for these), such as:

• I don't understand why we'd need to run the searchworks:prune_old_guest_user_data on all the VMs. This is a database cleanup task and probably should only be run VMs with the db role.
• The courses role may be unnecessary now the db role is assigned properly.

[corylown]

Closing this in favor of https://github.com/sul-dlss/SearchWorks/pull/4311