Add staggering of repository evaluation when a new repository is enrolled through auto-enrollment

[jhrozek]

Right now every repository registration also triggers evaluating of all the profiles defined in that project. With auto-registration, this can starve the tokens very fast.

We should develop a mechanism to stagger the repository reconciliations if e.g. more than 50% of the capacity of tokens is already depleted.

[evankanderson]

This probably needs a design, but before that, we should probably start monitoring our remaining tokens when calling GitHub, so we can see when we have a problem.

[mesembria]

Added #5124 to capture the work to add monitoring.