[ptg][cinder] backend drivers' day at the PTG

Hello Cinder third-party storage backend driver developers, maintainers, their managers, and any other interested parties: Thursday 22 April is Cinder Drivers' Day at the PTG. We kick off at 1300 UTC with Adam Krpan talking about his experiences deploying Software Factory to set up the third-party CI for Pure Storage. Anyone running an aging infrastructure for their third-party CI should be interested in this topic. See the Cinder project Xena PTG etherpad for the other Drivers' Day topics and the connection info to join the discussion: https://etherpad.opendev.org/p/apr2021-ptg-cinder