Configuration option to disable Missing Default Job email

[nicole-ashley]

I use default job functionality extensively to make sure that regular jobs are rescheduled once they complete. However an email is sent out for every job every time it's requeued, which creates a huge amount of spam and in my case pushed me over quota for my SendGrid account.

The only way to disable this email is to disable all queued jobs emails, but then I don't get important ones like job failures. A simple configuration property to disable these emails only but still receive failure notifications would be very useful.

[emteknetnz]

Sounds reasonable - if you'd like to provide a PR for this then I'm happy to look at getting it merged