[cinder] Stepping down from cinder core

Hi, I've been totally absent from the community in the last cycle, and unfortunately I'm not able to review Cinder patches in the next few cycles either. For this reason, I'm stepping down from the core team. Thank you all for the patience and attention to teach me so many things. It was a great opportunity for me to learn and grow professionally and personally. Hopefully sometime in the future I'll come back to the community again. Kind regards and stay safe, Lucio Seki