[cinder][stable] cinder-stable-core additions

Hi All,

After discussing with the current members of the cinder stable core team, I've decided to add the following members to the cinder stable core team.

1) Walter Boring - (Currently cinder core) 2) Sofia Enriquez - (Currently cinder core)

Sofia and Walt have been long term contributors in the Cinder project and I'm happy to have them as part of the stable core team. I will proceed with making changes to the stable core team[1].

[1] https://review.opendev.org/admin/groups/1b3ca2faf07b15efff426901a387eb7c9146...

Thanks and Regards Rajat Dhasmana