Based on the functionality by the following mods - 
weaker day zombie
zombies attack every entity

Enhanced Zombie AI

I was having issues with mods conflicting each other for the DayM-recrafted mod pack so I made my own. You are free to use it standlaone but it works best with the mod pack.

What it does

Sunlight - Applys Strenght I and Slowness III to all zombies in the sun. They won't chase you but if one sneaks up, they deal more damage

Horde mode - Attacking a zombie agros all zombies within a 10 block radius towards the player, both at day and night

Ruthlessness - Zombies attack all living entities i.e other passive mobs. Better protect your sheep farm

What it doesn't

This is a logic level mod, so you can safely add or remove this without breaking your save file. It's doesn't add any new mobs, just tweaks the AI of existing entites tagged with Zombie class (Husk, drowned)

Future of this mod

I love and appreciate you checking out this mod. I am no developer, coding isn't even part of my daily job. I just made this over the course of a week and don't really plan on updating or expanding it. As I said, it was made for a singuar purpose, the DayM-Recrafted modpack. If there is sufficent request for updating it for the latest minecraft version, I shall consider it.

You are free to use this in any modpack you like, a link back here is appreciated but not required. Thank you for your time