Draft: Deploy auto-deploy version of mailroom to production

What does this MR do?

!2909 (merged) was created and merged 2 months ago for Switch to using auto-deploy images of Mailroom (gitlab-com/gl-infra/delivery#19489).

The deployment on gstg and pre clusters (kubectl describe deployment -n gitlab gitlab-mailroom) and the dashboard for it look healthy.

Currently there are two QA issues gitlab-org/quality/quality-engineering/team-tasks#2032 and gitlab-org/quality/quality-engineering/team-tasks#2038 for testing mailroom so we should wait until they're done to deploy this change to production. Keeping this MR in draft mode until then.

Author Check-list

Please read the Contributing document and once you do, complete the following:

• Check if all of the following apply:
  • Assign to the correct reviewer per the contributing document
  • Apply the correct metadata per the contributing document
  • Link to related MRs for applying the changes on other environments
  • Link to related Chef changes
  • If necessary link to a Criticality 4 Change Request issue

Reviewer Check-list

• Check if all of the following apply:
  • Reviewed the diff jobs to confirm changes are as expected
  • No changes shown in the diffs not associated with this MR - This may require a rebase or further investigation

Applier Check-list

• Make sure there is no ongoing deployment for the affected envs before merging (see #announcements slack channel)