Schedule for runs

[mxxcon]

Please consider somehow adding an ability to schedule compression runs.
For example run it only once a day/week/month/whenever. That way active repos where images often change don't get flooded with commits from this bot.

[dabutvin]

This would be a great addition when we support a config file #2

Thanks for the issue!

[dabutvin]

I think offering daily/weekly/monthly as options is a good place to start.

In an effort to always keep ImgBot free by keeping costs super low I want to make sure not to clone repos on a schedule that have no activity.

One thing you can do in the meantime is to not delete the imgbot branch until you are ready for more image optimizations. We won't make a new PR if the old branch is hanging around.