I have actually written this feat already. It's called Second Attack, gives you two attacks with an attack action, and requires +3 proficiency bonus and either Strength 13 or Dexterity 13. Then there's the Third Attack feat, which requires Second Attack, +4 proficiency, and either Strength 15 or Dexterity 15; and Fourth Attack, which requires Third Attack, +6 proficiency, and either Strength 17 or Dexterity 17.
However, this is for a 5E variant that has no classes and everything is a feat. So everyone has to pay that, even people specializing in combat.