how can we make a % of zombie spawn as a boss mob

/summon zombie ~ ~ ~ {CustomName:'[{"text":"Zombie Brute"}]',Health:150,attributes:[{id:attack_damage,base:12f},{id:scale,base:2f},{id:movement_speed,base:0.5f},{id:max_health,base:150f}]} trying to make a feature that makes like 1-2% zombies spawn as a mini boss mob