I would do:
wget http://packages.openmediavault.org/public/pool/main/o/openmediavault-keyring/openmediavault-keyring_1.0.2-2_all.deb
sudo dpkg -i openmediavault-keyring_1.0.2-2_all.deb
sudo omv-aptclean repos
Well now apt update its not throwing anymore errors, i was looking for the keyring....deb file but I didn't know that i could find it on this address.
I did apply the setting and it worked finally. Thanks a lot