groups: Update membership for security-release-team
groups: Update membership for security-release-team

After discussing with PSC, we've decided to fork communications around
security releases into a separate mailing list -- security-release-team

Membership is restricted to:
- Product Security Committee
- SIG Release Chairs
- Patch Release Team
- Branch Managers

Signed-off-by: Stephen Augustus <f96984fef9637085f0559f1484dfd4e99545cd6e@vmware.com>

kubernetes/k8s.io,kubernetes/k8s.io,thockin/k8s.io,kubernetes/k8s.io,kubernetes/k8s.io,thockin/k8s.io,thockin/k8s.io,thockin/k8s.io