Don't want to write this by hand? GodCraft sets minecraft:body_rotation_always_follows_head for you with a switch.Get GodCraftOverview
minecraft:body_rotation_always_follows_head is an entity component: it goes in the components object of a custom mob, or in one of its component groups. Makes the entity's body always turn to face where its head is looking. It does nothing if minecraft:body_rotation_blocked is also on.
Example
Inside the components object of BP/entities/<name>.json (values are the defaults or placeholders):
BP/entities/<name>.json
{
"minecraft:body_rotation_always_follows_head": {}
}