Pass the namespace to `kubectl apply` in `deploy:secrets`

What does this MR do and why?

We were creating/updating the secrets in the default namespace without this change. 🤦🏼

I discovered this as part of https://gitlab.com/gitlab-com/gl-security/security-department-meta/-/issues/1463#note_1143301099.

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