Is it planned to have armors that works better against bullets than against melee weapons and armors that work better against melee weapons ?

No. I don’t know what you’re talking about.

apparently yes.
on the admin site all the armours have parameters that change how much they protect from melee and from bullet

Yes this is what they are planning. There will be set perimeters in the game that armor protects so much against each type of damage. Gunshots would be one type melee another fire another and so on. They could move even farther with this if they wished to make it so slashing bludgeoning and piercing is each it’s own type of damage. The final thing they have with the new targeting system is, certain places on the armor will protect more then others. This means if you have a metal plate where the plate is at is the protected area while the rest is unprotected.

A video to show you:

Hope that clears things up for you.