Add em for backend and frontend for group certify

What does this MR do and why?

Describe in detail what your merge request does and why.

While checking !1649 (merged)

There is a related issue open here.

Using backend_engineering_manager frontend_engineering_manager is a workoround.

If we use engineering_manager, then the EM will not be mentioned is reports.

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review