I would like to have some sort of gift that you can give to iron golems that spawned by villagers to make them become passive to players.

My suggestion is that: they love holding poppy right, then how bout rose? Since roses got removed years ago, maybe have some sort of bouquet of rose that you can give to the golem to pacify them. The bouquet can't be crafted and is found randomly in villages.

Golems are already passive if you don't attack them. The only other reason they attack is if you've been beating up villagers, like, a lot.