Update SRE hiring process
Updating SRE hiring process to follow: https://gitlab.com/gitlab-com/people-ops/hiring-processes/blob/master/Engineering/Infrastructure/Site-Reliability-Engineer/Interview-Process.md
Updating SRE hiring process to follow: https://gitlab.com/gitlab-com/people-ops/hiring-processes/blob/master/Engineering/Infrastructure/Site-Reliability-Engineer/Interview-Process.md