Parameterize Fast+Guard cutoffs
With jnewsome/sponsor-61-sims#17, tpo/network-health/analysis#41 (closed), and jnewsome/sponsor-61-sims#18, we can determine new threshholds for Fast+Guard relays, and see if this improves performance and reduces queue overload.
Basically, we want to make consensus parameters for the fast+guard percentile cutoffs, and determine new values for them.
This should be done in tandem with #40642 (closed), and jnewsome/sponsor-61-sims#16.