instant_finalists_amount is the amount of teams that instantly are in
the finals after the group stage ends.
intermediate_round_participants_amount is the amount of teams that have
a chance to advance after group stage but must play a relegation game to
actually do so.
Both of these values need to match, so that
instant_finalists_amount + (intermediate_round_participants_amount / 2)
is a power of 2. Or to be more precise, the power of two that is saved
in playoff_teams_amount of the tournament.
