Backport '4699-fix-backup-job-mount' into '6-11-stable'

What does this MR do?

Merge branch '4699-fix-backup-job-mount' into '6-11-stable'

Mount the microsoft_graph_mailer client secret in the backup-job pod

Closes #4699

See merge request https://gitlab.com/gitlab-org/charts/gitlab/-/merge_requests/3168

Merged-by: Jason Plum <jplum@gitlab.com>
Approved-by: Jason Plum <jplum@gitlab.com>
Reviewed-by: Jason Plum <jplum@gitlab.com>
Co-authored-by: Jason Young <jyoung@gitlab.com>

(cherry picked from commit 28368b05322648c4f4aeb3f497fe08b43e802146)

f9e76b4a Mount the microsoft_graph_mailer client secret in the backup-job pod
a8d879d0 Add a test for microsoft-graph-mailer-client-secret mounts
fb48751c Fix cop
d0b9a648 Dry up the spec by using existing helpers
4109d033 Fix applied suggestion

Related issues

Relates to #4699 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.