`schedule.interval` support cron expressions

[jlosito]

I would like the ability to schedule dependabot, schedule.interval, on more options other than daily, weekly, and monthly.

For my use case specifically, I am looking for schedule it quarterly and semi-annually.

Rather than adding options quarterly and semi-annual, I believe it would be much better if dependabot were allowed to be scheduled using a cron expression to make it more generic. This would allow users to schedule it all kinds of different ways that better fit the user's needs.

[jeffwidman]

Thanks for the idea.

[ivan-penchev]

I have an similar issue as #2038 as I want to run it "biweekly".
Support on cron would be must appreciated.

[gildor]

biweekly/fortnight is a pretty useful interval because many companies do 2-week sprints.
But I think cron is a much better and more flexible option.
I would suggest having schedule.cron property and fail if schedule.interval also present