Isn't it more or less automated? Create an Aurora replica cluster from your normal RDS database, switch your application over and then delete the old RDS instance.
what if your postgres instance has replicas?
They support blue/green for RDS postgres, but not for RDS/Aurora.
It's slated for later next year is what I heard.
I did it it was the craziest process but it worked eventually even though that was quite a while ago.
Literally just today I was looking into a new project that requires postgres, and read on the aurora doc that this exists. Didn't look further into it considering the project is new and no migration is involved, but if you need this, worth searching.