FOUND A SOLUTION BY MYSELF AND WANT TO SHARE IT WITH YOU GUYS!
So to be honest I totally gave up on this issue and accepted the fact that all my photos are lost.
But as a last possibility I opened up the phone, disconnected the front camera flex cable and connected the phone to my Mac.
Again iTunes told me that the phone had to be restored/updated in order to work again.
So I hit the "Update" button and
BOOOOOM
it successfully installed iOS 11.4 and my phone came back to life.