In all of our current uses of os.umask or filesystem.umask, we always temporarily set it to a different value and then restore it using a try/finally block. I expect this pattern to continue.

Because of that, why don't we create a simple function in certbot.util that can be used as a context manager to set umask to a value and restore it to its previous value when exiting the with blo

It could be useful to allow for controller's sync period to be configurable.

Background:
See Kubernetes sample controller diagram for reference. cert-manager's controller consists of a number of control loops that sync various cert-manager's and Ku