Consider Fcron migration schedulers/tools

[mtai]

I believe our target audience would be people using fcron right now. To ease a transition, we may want to consider an "FcronScheduler" that could parse the semantics of a traditional "Fcron line". Alternatively, we could provide a tool that would convert an Fcron line into whatever scheduler someone would expect:

FcronScheduler could take and run a job at 12:30 everyday 00 30 * * *

OR, user runs a command rephrase_fcron "00 30 * * *" that spits out the equivalent Tronfig scheduler

schedule: !DailyScheduler start_time: "00:30:00"

OR

schedule: !IntervalScheduler interval: "2 mins"

[rhettg]

I originally pushed back on this idea (mtytel proposed it a while back) in that most of the complexity of our fcron rules comes from trying to handle situations by complex timing that should really be done by some smarter tool (like measure system load, queues, etc)

However, I can see this being necessary to move more stuff over prior to us having those tools in place.