Update security release merge_request_template re: AppSec approvals
This merge request is meant to make it more clear as to which AppSec team member should be pinged for review and approval for security issues.
This is a followup MR to gitlab-org/release/docs!272 (merged) as well as gitlab-org/release/docs!279 (merged)
I'm adding the WIP label until gitlab-org/release/docs!279 (merged) is merged, since the Code reviews and Approvals section needs to be updated before this change goes in.
Edited by Andrew Kelly