[CAL-3100] Round Robin Fairness Algorithm

[CarinaWolli]

Stop assigning to a user when a given fairness threshold is reached, even if this person is the only possible assignee, if it is determined unfair we disable this user.

Example:
If a round-robin host is assigned to more than 5 bookings more than the other round-robin hosts, their availability won't be shown and they can't be booked.

Things to consider:

• This will make debugging availability issues more complex, we should think about adding something to help debug missing slots disabled because of fairness.
• How to deal with newly added hosts: If a host is getting added when other hosts already have a lot of bookings the new host can be booked many times until they reach this amount of bookings. This is not ideal and should be handled differently

_{From SyncLinear.com | CAL-3100}

[joeauyeung]

@CarinaWolli to ensure that we're meeting the requirements found in this doc

[CarinaWolli]

@CarinaWolli to ensure that we're meeting the requirements found in this doc

I think this is what we want instead: #15340