[cinder][stable] proposing Rajat Dhasmana for cinder-stable-maint team

Rajat Dhasmana (whoami-rajat on IRC) has been organizing the cinder project's stable releases for a while now, and has also been active reviewing backports. He has a good understanding of the OpenStack stable maintenance policy and has been a reliable cinder core reviewer since January 2019. I hereby propose that he be included as a member of the cinder-stable-maint team. cheers, brian